Muslims believe that Muhammad is a prophet. There were several prophets but he is believed to be the greatest among them, as well as the most recent one. He managed to unify most of Arabia under Islam in 630. He didn't know he was destined to be a prophet in the beginning, however. When he turned 40, he began to receive revelations from Allah, that helped formed the Quran and the fundamentals and foundation of Islam.
When someone is becoming Muslim, praying, going through a hardship, or simply saying it, Muslims say, "There is no God but Allah, and Muhammad is his messenger". They most often say it in Arabic.
Prophets are also known to perform miracles, and he performed many himself. One miracle that was seen by numerous amounts of people was when he produced water from his hands. He was traveling with a large group (I think it was hundreds of people) and they ran out of water.
Hopefully, this helps! Let me know if you need more information of a specific topic. I just gave a general explanation. :)
