"All you do is study so that you can learn enough to be smart enough to be able to buy a goddamn Cadillac some day."
"Now, listen," old Sally said. "Lots of boys get more out of school than that."
"I agree! I agree they do, some of them! But that's all I get out of it. See? That's my goddamn point," I said. "I don't hardly get anything out of anything."
1.Here Holden is talking how much he thinks school is crap and how much he doesn't like it. He really hits a bulls eye when he talks about the Cadillac. If you think about it that's the 2nd best reason to take a job, (besides just liking the work) and Holden is really disgusted with this.
2.Well it really gives us a direct quote from Holden saying what he thinks about education for him. Before this he had mostly just alluded to it.
3.So, kind of what I said above. But also I think it shows us that Holden is subconsciously trying to drive girls other than Jane away because for no other reason would he just push Sally away like that.