In Islam, Allah is the only one real supreme being, all-powerful and all knowing Creator, Sustainer, Ordainer, and Judge of the universe.
Allah is name of Almighty God in Arabic a sister language of Aramic the Language of Jesus Christ (peace be upon him). All the Christian and all version of Bible used Allah for Almighty God in Palestine , Lebnon, Syria since 2000 years even earlier than Islam.
Islam puts a heavy emphasis on the conceptualization of God as strictly singular (tawhid). Allah is arabic name of Almighty God. It is same God which has been worshiped by all the prophets of Almighty God, Noah, Abraham, Issac, Ishmael, Jacob, Moses, David, Zackaria, John the Baptist, Jesus. and the last Prophet of God Mohammad (peace be upon them all).
The God of Prophet Jesus Christ and Allah are not diffrent. Infact currently Arabic and original Aramic bible uses same word Allah for God almighty for the last 2000 years. Aramic was the original language of the Prophet Jesus Christ (peace be upion him). The first thing Islam asserts and the last is that there is no god except Allah. Allah being the primary name of God in Arabic and meaning ‘the god’.
Almighty God (Allah) is unique (wahid) and inherently one (Ahad), all-merciful and omnipotent. All these names refer to Allah, the supreme and all-comprehensive divine name. Among the 99 names of God, the most famous and most frequent of these names are “the Compassionate” (al-Rahman) and “the Merciful” (al-Rahim). , everything in the world is a sign of God we can see only the activities of God and cannot see God.
How We Know the existance of God Almighty
Universe, Earth and life on earth is not an accident. Accidents can never create a well coordinated, disciplined , balanced, perfect in all sense and astonishingly complex and beautiful world. The beautiful wonders of creation is actually inevitable and irrefutable proof of existence of its creator The God almighty. God himself invite human being to ponder indepth about the creation of oneself and day and night, animal and birds, sun and earth , rain and sky. God mentions in the Quran several times that you eye will return and you will not find any imperfection in his creation.
“Blessed is He in Whose Hand is the dominion, and He is Able to do all things. (1) Who has created death and life, that He may test you which of you is best in deed. And He is the All-Mighty, the Oft-Forgiving; (2) Who has created the seven heavens one above another, you can see no fault in the creation of the Most Gracious. Then look again: “Can you see any rifts?” (3) Then look again and yet again, your sight will return to you in a state of humiliation and worn out (4)” (Almulk- 67 1-4)
Existance of Almighty is undeniable fact.
Why we can not see Him:
God almighty is so supreme and beyond our limited five senses comprehension and our very limited ability to visual observation. So God insists several places in Quran to believe His existence by His creation not by demand of seeing him. It is just like an ant can not see a huge mountain. So should Ant deny presence of Mountain?.
Creationist and Darwinists
Can any body tell me? Who has made the perfect, mathematical and complex laws of Physics, laws of Chemistry and laws of biology , complex reproductive system in human and animal and plants ?. Scientists are only discovering these laws and in through obeying these law making some imperfect or semi perfect things. Yet the scientists have discovered a tiny part of the Creator’s innovative world. 99% yet to be explored. Keeping in view only a stupid or illogical persons can deny the perfect, and the wise Creator.
The Darwin has proposed a theory not fact . His tautology could not be proved by any undoubtedly/real true scientific evidence/fact. After studying 10,000 fossils, Harun Yahya (click here to explore) a Turkish biologist has challenged all Darwinists of the world to produce a single intermediate fossil, he will pay US$100 billion . He has proved that every species appeared in perfect shape and disappeared and new specie appeared in perfect shape. No incomplete bird can survive and incomplete eye can see. A half build eye and half build wing cannot see and cannot fly.
Survival of the fittest? Why love existence? Why a mother dies for her child?, Why A perfect family system of Honey bee functions?. Why Peacock beautiful colors appeared?. Darwinists have failed miserably to explain the facts of creation. So fact of existence of creator of a perfect, very beautiful and complex creation is just like Sun on the sky but blind cannot see.
Indeed Creation and ordering of the universe is seen as an act of prime mercy for which all creatures sing God’s glories and bear witness to God’s unity and lordship. According to the Islamic teachings, God exists without a place. According to the Qur’an, “No vision can grasp Him, but His grasp is over all vision. God is above all comprehension, yet is acquainted with all things” (Qur’an 6:103)
Almighty God Loves all His Creatures
God in Islam is not only majestic and sovereign, but also a personal God: According to the Qur’an, God is nearer to a person than his jugular vein. God responds to those in need or distress whenever they call. Above all, God guides humanity to the right way, “the holy way .”
Islam teaches that Allah is the same god worshiped by the members of other Abrahamic religions such as Christianity and Judaism (Quran 29:46).
Oneness of God
Oneness of God or Tawḥīd is the act of believing and affirming that God (Arabic: Allah) is one and unique (wāhid). The Qur’an asserts the existence of a single and absolute truth that transcends the world; a unique and indivisible being who is independent of the entire creation. According to the Qur’an: “Say: He is God, the One and Only; God, the Eternal, Absolute; He begetteth not, nor is He begotten; And there is none like unto Him.” (Sura 112:1-4, Yusuf Ali)
Thy Lord is self-sufficient, full of Mercy: if it were God’s will, God could destroy you, and in your place appoint whom God will as your successors, even as God raised you up from the posterity of other people.” (Sura 6:133, Yusuf Ali)
The Qur’an also provides a monist image of God by describing the reality as a unified whole, with God being a single concept that would describe or ascribe all existing things:”God is the First and the Last, the Outward and the Inward; God is the Knower of everything (Sura 57:3)” Some Muslims have however vigorously criticized interpretations that would
lead to a monist view of God for what they see as blurring the distinction between the creator and the creature, and its incompatibility with the radical monotheism of Islam.
The indivisibility of God implies the indivisibility of God’s sovereignty which in turn leads to the conception of universe as a just and coherent moral universe rather than an existential and moral chaos (as in polytheism). Similarly the Qur’an rejects the binary modes of thinking such as the idea of duality of God by arguing that both good and evil generate from God’s creative act and that the evil forces have no power to create anything. God in Islam is a universal god rather than a local, tribal or parochial one; an absolute who integrates all affirmative values and brooks no evil.
Tawhid (Monothism )constitutes the foremost article of the Muslim profession.  To attribute divinity to a created entity is the only unpardonable sin mentioned in the Qur’an.  Muslims believe that the entirety of the Islamic teaching rests on the principle of Tawhid. 
Almighty God’s attributes
The Qur’an refers to the attributes of God as God’s “most beautiful names” (see 7:180, 17:110, 20:8, 59:24). According to Gerhard Böwering, “They are traditionally enumerated as 99 in number to which is added as the highest name , the supreme name of God, Allāh. The locus classicus for listing the divine names in the literature of qurʾānic commentary is 17:110, “Call upon God, or call upon the merciful; whichsoever you call upon, to him belong the most beautiful names,” and also 59:22-24, which includes a cluster of more than a dozen divine epithets.” The most commonly used names for god in Islam are:
The Most Gracious
The Most Merciful
The Ever Forgiving
The Ever Providing
The Lord and Cherisher of the Worlds
The Self Subsisting (upon whom all creatures depend for sustenance)
The Eternal Lord (who never dies)
The Supremely Wise
The Guardian of faith
Furthermore, it is one of the fundamentals in Islam that Almighty God exists without a place and has no resemblance to his creations. For instance, God is not a body and there is nothing like him. In the Quran it says what mean “Nothing is like him in anyway,” [see Quran 42:11]. Allah is not limited to Dimensions.
The Qur’an describes God as being fully aware of everything that happens in the universe, including private thoughts and feelings, and asserts that one can not hide anything from God:
In whatever business thou mayest be, and whatever portion thou mayest be reciting from the Qur’an,- and whatever deed ye (mankind) may be doing,- We are witnesses thereof when ye are deeply engrossed therein. Nor is hidden from thy Lord (so much as) the weight of an atom on the earth or in heaven. And not the least and not the greatest of these things but are recorded in a clear record.—[10:61]
Some western scholars[who?] have suggested that Muhammad used the term Allah in addressing both pagan Arabs and Jews or Christians in order to establish a common ground for the understanding of the name for God, a claim Gerhard Böwering says is doubtful.
God in Islam vs God in pre-Islamic Arabian conceptions In contrast with Pre-Islamic Arabian polytheism, God in Islam does not have associates and companions nor is there any kinship between God and jinn.  Pre-Islamic pagan Arabs believed in a blind, powerful, inexorable and insensible fate over which man had no control. This was replaced with the Islamic notion of a powerful but provident and merciful God.
God in Islam vs God in Judaism
The Qur’an insists, Muslims believe, and historians affirm that Muhammad and his followers worship the same God as the Jews [see Qur’an 29:46].
The Quran’s Allah is the same Creator Almighty God who covenanted with Abraham”. Qur’an portrays Allah as both more powerful and more remote than Yahweh, and as a universal deity, unlike Yahweh who closely follows Israelites. (Similar to Yahweh : in Arabic ” Ya Hoowa” means ” O! That is He ” . Quran uses term ” Hoowa” several hundred times to refer to Almighty God Allah. Since Hebrew is sister language of Aramic and Arabic hence Yahoweh has same meaning as “Ya hoowa” in Arabic i.e. “Calling He”
Almighty God, says the Qur’an, “loves those who do good,” and two passages in the Qur’an express a mutual love between God and man, but the Judeo-Christian precept to “love God with all thy heart” is nowhere formulated in Islam. The emphasis is rather on God’s inscrutable sovereignty, to which one must abandon oneself. In essence, the “surrender to Allah” (Islam) is the religion itself.
God in Islam vs God in Christianity
Islam vigorously rejects the Christian belief that God is three persons in one substance (see Trinity). In the Islamic conception of God, no intermediaries between God and creation exists and God’s presence is believed to be everywhere, and yet he is not incarnated in anything.
The Christian West perceived Islam as a heathen religion during the first and second Crusade. The traditional view of Christianity however was that Muhammad’s God is the same as Jesus’ God. All Christians living in Syria Lebnon use Allah for God. All versions Bible in Arabic word Allah is used for God Almighty in Syria and Lebnon, Plastine for the last 2000 years even before apperance of Prophet Muhammad. Ludovico Marracci (1734), the confessor of Pope Innocent XI, states: Numerous passages in the Old testament refer to God’s love. A central theme in the New Testament is God’s love in sending of Jesus.
In Islam, Almighty God’s love and presence is proved through his signs in our ownself, creation of men, creation of animal being, a well coordinated, perfact and intelligently designed physical world and the creation of the Earth and sky where humans can live in moderate comfort.
“O ye people! Adore your Guardian-Lord, who created you and those who came before you, that ye may have the chance to learn righteousness;Who has made the Earth your couch, and the heavens your canopy; and sent down rain from the heavens; and brought forth therewith fruits for your sustenance; then set not up rivals unto God when ye know (the truth).” (Sura 2:21-22, Yusuf Ali)
The most common Muslim invocation of God is ‘the Most-Gracious, the Most-Merciful’. Two other of the “beautiful names” of God are ‘the very Loving’ (wadud) and ‘the constant giver'(wahhāb). In Islam, Watt says, God has provided the opportunity for each community to attain the great success (i.e. the life in Heaven) by sending messengers or prophets to them. Islam has also has a doctrine of intercession of Muhammad on the Last Day that would be received favorably, though the sinners might be punished for their sins either in this life or for a limited time in hell.