Islam teaches that it is a lot better to be a pacifist than to be aggressive. There is a concept of "Jihad", or holy war, but some Muslims take it the wrong way and since the west is predominantly Christian, they see it as suppressing the teaching of Islam, and try to destroy the face of the west (America). This holds true for a very small percentage of Muslims. Most of the ones that I know, myself included, blame the misconceptions on the media. Specifically, I'd say Fox News is the most untrustworthy source of information, but a couple other new channels and newspapers tell the world some things about Islam out of context, or just flat out lies.
Islam teaches that there were 24,000, including Jacob, David, Noah, Abraham, Ishamael, and Jesus, and that the last and most important was Muhammad. There are also 4 Holy Books, the first being the Torah, the next was the original Psalms, after that the original Gospel, and finally the Qur'an. It says that the first three books were only for a set time period, and that the Qur'an is from when it came around, about 1400 years ago, to the Day of Judgement, the last day on Earth. It says that whenever mankind forgot about its purpose, a prophet, or messenger, was chosen to remind the whole of humanity that there is only one God, that He created all of us, and that we must worship Him, for it is to Him that we will are return.
Now, as the religions continued, changes were made. Women had to be covered up (don't get me started on how it IS NOT sexist), the main prayer was changed from Sunday to Friday, prayer was mandatory five times a day, everyday, and a few other things. I think that people who haven't converted to Islam, yet truly believe in one God and that they are obeying His rules, are still Muslims, as the literal meaning of the word is "one who has submitted to God"
Now, I'm by no means an expert in my religion, but I think I hit most of the main points.