The Gospels are the first four books of the New Testament, they deal with what Christians believe Jesus did. The gospels like the rest of the Bible are supposed to be inspired by God. Despite this the four books sometimes contradict each other.
One possible reason for the discrepancies between the four canonical gospels is that they were intended for different audiences. They were never intended to be published side-by-side and studied together. Each gospel has its own emphasis which points to its intended audience.
- Matthew, which contains many references to the fulfillment of Old Testament prophecy, was likely aimed at Jews who wanted "proof" that Jesus was the Messiah.
- Mark is considered the "action gospel" because it portrays Jesus as a decisive, consistent man of action. This would have appealed to those who objected to the capricious nature of the Greco-Roman polytheistic gods and goddesses.
- Luke, which has the highest quality writing of the four gospels, was probably written for educated Greeks, Romans and other upper-class gentiles.
- John, being the most mystical and least "preachy" of the four canonical gospels, was likely written for like-minded pagans who were turned off by prophecy, theology, and rules.
Today, you can often tell how hard-line a Christian is by which gospel he or she favors. From most liberal to most conservative, the progression is (arguably) John - Mark - Matthew - Luke.
There are also any number of Non Canonical Gospels which weren't included in the New Testament because they went against the Faith of those who assembled the New Testament.
Incorporates material from RationalWiki