When you understand what's being spoken, it's entender. When you understand that and more, it's comprender. Or, when you understand it literally, it's entender, but when you understand its figurative connotations, it's comprender.

What is the difference between Comptido and Entiendo?

There's not a real meaning difference, and both are equally formal and informal. It's just that "entender" is more used than "comprender".

What Entiendes mean?

(you) understand, (?) do you understand, get.