Ever have someone tell you a joke and but you don't quite get the punchline? And then two seconds later you blurt out, "Oh, I get it". Of course you have.
Well, when that happens to you in your next Spanish conversation, you can shout out "¡Ya caigo!"
Anytime you would use "I get it" in English, you can use "Ya caigo" in Spanish. And if you need to say "I don't get it" you can say "No caigo".