The most fundamental belief that a Muslim has is that "There is only One God," the Creator, the Sustainer -- known in the Arabic language and by Muslims as Allah. Allah is not a foreign god, nor an idol. Arabic-speaking Christians use the same word for the Almighty.
The fundamental pillar of faith in Islam is to declare that "there is no deity worthy of worship except the One True Almighty God" (in Arabic: "La ilaha ill Allah").
In the Qur'an, we read that Allah is Compassionate and Merciful. He is Kind, Loving, and Wise. He is the Creator, the Sustainer, the Healer. He is the One who Guides, the One who Protects, the One who Forgives. There are traditionally ninety-nine names, or attributes, that Muslims use to describe Allah's nature.
Some non-Muslims mistakenly think that Allah is an "Arab god," a "moon god," or some sort of idol. Allah is the proper name of the One True God, in the Arabic language used by Muslims all over the world. Allah is a name that is neither feminine nor masculine, and it cannot be made plural (unlike god, gods, goddess, etc). Muslims believe that there is nothing in the heavens nor on earth that deserves worship except Allah, the One True Creator.
Islam is based on the concept of Tawhid, or Unity of God. Muslims are strictly monotheistic, and fiercely reject any attempt to make God visible or human. Islam rejects any form of idol worship, even if its intention is to get "closer" to God, and rejects the Trinity or any attempt to make God human.
"Say, 'He is Allah, the One;
Allah, the Eternal, Absolute;
He begets not, and neither is He begotten;
And there is nothing that can be compared to Him."
"When My servants ask thee concerning Me,
I am indeed close (to them).
I respond to the prayer of every suppliant
when he calls on Me.
Let them also, with a will,
Listen to My call, and believe in Me,
that they may walk in the right way."
Islam is a natural faith, a religion of responsibility, purpose, balance, discipline, and simplicity. To be a Muslim is to live your life remembering God and striving to follow His merciful guidance.