I have understood
No he entendido nada de lo que has dicho.
I haven't understood anything you've said.
A ver si lo he entendido bien.
Let's see if I understood correctly.
¿Crees que no he entendido lo que acabas de decir?
Do you think I didn’t understand what you just said?
— El duelo (2006)
I understood the puzzle.
Let's see if I've got this straight.
I barely understood anything.