In the second paragraph of the story, we learn that when George stays cooped up in his room all alone, he's sometimes listening to sports on his radio, but he's mostly reading. More specifically, he's reading easy, nonfiction content: a reference book, plus some magazines and newspapers. Here's how the narrator describes what George does during all those solitary hours:
But most of the time he sat in his room. In the afternoons he listened to the ball game. Otherwise he had a couple of old copies of the World Almanac he had bought long ago, and he liked to read in them and also the magazines and newspapers that Sophie brought home, that had been left on the tables in the cafeteria. They were mostly picture magazines about movie stars and sports figures, also usually the News and Mirror.
Because George is only reading the things that he happens to already own, or the things that happen to be in the house, it's clear that although he's intelligent enough to read and be interested in some things, he definitely hasn't taken charge of his own life. He's basically hiding from the world and hiding from his own shame of not having finished school. Fiction gets on his nerves, possibly because it's all about adventures and excitement that he'll never have, so he doesn't read that. And "worthwhile books" are difficult for him and frustrate him, so he doesn't read those, either.
All this sounds rather bleak, doesn't it? But keep in mind that this is just the first few paragraphs of the story; they're revealing George's problem. As the story unfolds, he'll have a chance to change his habits, and to change his life for the better.