I was responding to a thread on a Christian forum about what Islam is and came up with the following. I thought I would cross-post over here.
The word Islam means, "to submit". The word Muslim means, "one who submits".
Muhammad was a man who claimed to have a "vision" but wasn't sure if it was real and so he asked his "Christian" wife who confirmed it for him as did her cousin.
Allah was the name used for God by Jews and Christians at the time and actually means "the God" emphasizing a monotheistic belief.
There are several different sects of Islam: Sunni, Shi'a, Sufi.
The majority of Muslims are Sunni and include Muslims in Palestine, Lebanon, Egypt, Jordan, and Saudi Arabia. Shi'ites are Iranians and Iraqis. Sufis are spread out, but a good number are in Turkey and Pakistan. Sufis are considered the mystics and often seek to become "one" with God. One could call them the "charismatics" of Islam.
Muslims follow 5 pillars. Recitation of Shahada (There is no god but Allah...), pray 5 times a day, alms-giving, pilgrimage to Mecca (Hajj), fasting during Ramadan.
Some will say Jihad (Holy war/struggle) is a 6th pillar, but that's extremely debatable. The pillars are not found in the Qur'an, but in the Hadith (traditions).
The Qur'an can really be broken up in two parts, Meccan and Medinan.
The early years were spent in Mecca and were largely peaceful and can be seen in the early parts of the Qur'an if one were to put it chronologically. The latter years were Medinan, in which he had finally become a powerful leader and the Jews and Christians finally started coming against him. One can see that in the writings of the later parts of the Qur'an, chronologically.
Sharia law comes from the Hadith (traditions) which are sayings of Muhammad, Aisha, and/or other disciples of Muhammad. In fact, many Muslims follow the Hadith more than the Qur'an. Most Muslims do not know exactly what the Qur'an says, even though many may have memorized as a young child.
Many Shi'ites also follow a branch called the Twelvers. Meaning which there are 12 Imams, the 12th of which disappeared and is expected to return again. Ahmadinejad of Iran is one of these, which may explain a lot of his words and actions.
On the concept of Jihad, there are three views:
1) Inner struggle - fighting within oneself to keep oneself pure