What does the quote "He didn't get it" mean in chapter six of The Great Gatsby?
The quote to which you refer is found in Chapter 6 when Nick gives the reader some background on Gatsby's past. The reader discovers that Gatsby learned how to be a rich person from Dan Cody, a millionaire who earned his money from "the Nevada silver fields,...the Yukon,...every rush for metal since seventy-five." Gatsby saved Cody from crashing his yacht into the shallow shores of Lake Superior, and in return, Cody hired him as a personal assistant. For five years, Gatsby worked for Cody, and from him, "He was left with his singularly appropriate education; the vague contour of Jay Gatsby had filled out to the substantiality of a man."
However, the reason Gatsby only stayed for five years was because Dan Cody "inhospitably died" one evening when Ella Kaye, "the newspaper woman," showed up. And while "it was from Cody that he inherited money—a legacy of twenty-five thousand dollars. He didn’t get it. He never understood the legal device that was used against him, but what remained of the millions went intact to Ella Kaye." Gatsby never saw any of the money that Dan Cody left to him, so he was left again as a penniless young man, but this time, he knew how to live and work with wealthy people. At this point in the book, then, the reader still does not know where Gatsby earned the extravagant money he flaunts, but the reader starts to understand why Gatsby acts the way he does (no drinking—he learned that Dan Cody lost control when he drank).