Prophets are people who said that God or gods talked to them. They freely teach other people what they learned. Most of them warn people that something very good will happen if they change their lives.
For the main Abrahamic religions, there are two kinds of prophets, major and minor. Major prophets gave a lot of teachings while minor just re-teach things other prophets taught or they do not have many teachings. For example the most notable prophet is Muhammad the founder of Islam.