1. "Muslim" and "Arab" are not the same thing.
"Muslim" is a religious term. A Muslim is someone who adheres to the religion of Islam. "Arab," on the contrary, is an ethno-linguistic term. An Arab is a member of the people group who speak the Arabic language. It is true that Islam originated among the Arabs, and the Qur'an was written in Arabic. However, some Arabs have historically been part of the ancient orthodox Christian churches. On the other hand, Islam spread far beyond the Arab world, and today most Muslims are not Arabs. This includes the Turks, the Kurds, the Iranians, the Pakistanis, other South Asian Muslims, the Malaysians and the Indonesians, almost all of whom are Muslim but none of whom is Arab.
2. The word "Islam" means submission.
A Muslim is someone who submits to God. The Islamic conception of who God is, and how he is to be worshiped and served, is based on the teaching of Muhammad. Thus the Islamic creed is: "There is no God but God, and Muhammad is his prophet."
3. There are two major denominations of Muslims.
The two major denominations of Muslims are Sunni and Shi'a. Sunnis are the vast majority, at 85 percent of all Muslims. The split occurred in the first generation after Muhammad's death and was based on a dispute over who should succeed him as leader of the Islamic community.
READ MORE: http://thegospelcoalition.org/blogs/tgc/2013/07/05/10-things-every-christian-should-know-about-islam/