Matthew, Mark and Luke are called the synoptic (looking together) gospels. Mark was the first written, Matthew and Luke came a short time later and expanded on the story.
John was written much later, towards the end of the first century. It has a very different, more intimate, feel to it, probably because John was a member of Christ's inner circle.
Erasmus was the first known individual to claim that the Hebrew version of Matthew was not first, so I would be cautious about following the two-source hypothesis very closely without examining what was unanimous for 1500 years.