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 live good lives. Or if they sin, God will punish them. Sometimes people who are not religious are also called prophets if they correctly predict the future. Persons who think bad things will happen are sometimes made fun of as being "prophets of doom". A person who says things will happen, but they don't happen are called "false prophets".
For the main Abrahamic religions, there are two kinds of prophets, major and minor. Major prophets gave a lot of teachings while minor prophets do not have many teachings. The most important prophet in Judaism is Moses. Isaiah and Elijah are also important. Elijah didn't write any books in the Bible but did many miracles and told kings that God would punish them.
In Christianity Jesus was the main prophet. Other Christian prophets are mentioned in the New Testament, both men and women. John, a disciple of Jesus wrote the Book of Revelation which has many prophecies.
In Islam, Muhammed is considered the greatest and last prophet. Muslims also consider Moses and Jesus to be prophets and many others who lived before the time of Muhammed. Some modern religions say that their founder is a prophet, such as Joseph Smith. The famous preacher Billy Graham is sometimes called a prophet.