"Exactly," said Harry. "And we know you get in using those funny coins, or tokens, or whatever they are, because I saw that witch borrowing one from here friend -"
Harry Potter and the Deathly Hallows
I looked up "get in", but it seems to me that none of definitions could fit for the context. If I have to guess, I think it probably means to succeed in doing something. However, I don't know if I'm getting it right. Is it a common usage? What does it truly mean?