"Righteous is he who believes in Allah and the Last Day and the Angels and the Scriptures and the Prophets." -- Quran 2:177
There is no official creed to which one must adhere to be considered a Muslim. All that is required is to believe and recite the Shahada: "There is no God but God, and Muhammad is his Prophet." Beyond this core belief, however, Muslim doctrine is often summarized in "Six Articles of Faith." Many Muslims believe that one must adhere to the six articles to be considered a Muslim.
The single most important belief in Islam, and arguably the central theme of Islam, is that there is only one God. The name of God is Allah, which is simply Arabic for "the (al) God (Ilah)." The term is related to Elohim, the Hebrew word for God.
Muhammad, the founder of Islam, is revered as "the Seal of the Prophets" - the last and greatest of the messengers of God. He is not divine in any way, for the strict monotheism that characterizes Islam (as well as Judaism) does not allow for such an interpretation. Other prophets are important in Islam as well, all of which are shared with the Jews or the Christians.
According to the Qur'an, Allah "created man from a clot of blood" at the same time he created the jinn from fire. Humans are the greatest of all creatures, created with free will for the purpose of obeying and serving God.
For a Muslim, the object of life is to live in a way that is pleasing to Allah so that one may gain Paradise. It is believed that at puberty, an account of each person's deeds is opened, and this will be used at the Day of Judgment to determine his eternal fate.
Like Christianity, Islam teaches the continued existence of the soul and a transformed physical existence after death. There will be a day of judgment and humanity will be divided between the eternal destinations of Paradise and Hell.
The Qur'an is clear that there must be "no compulsion in religion" (2:256). Yet Islam is not indifferent to conversion either - Muslims consider their religion to the be the one true religion, and invite people of all races, nationalities and religions to be part of it.