What does "get the idea" mean?

Vocabulary Word: get the idea

1. Definition (expr.) understand

Examples I don’t get you. You say one thing and do another.

Examples I’d like to figure out this math problem before school tomorrow.

Examples I didn’t understand the game at first, but now I think I get the idea.

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Antarctica

There is only ”get” in the first example. Do I need the word “idea” as well? So I haven’t got the slightest IDEA about it :(