What do we learn about Gatsby's background here? Why is this important?

In the novels, Gatsby lied to Daisy about his background (that he's a well educated self-made man) because he thought that daisy was one of the "luxurious" type of women.

In order to convince her that he's good enough for her, he went to oxford to gain education after the war, but Daisy already married to Tom Buchanan.