Get your head round something
Definition 1 of 1
Pro Tip 1/3Colloquial Use
Used in casual conversation, not suitable for formal writing or presentations. 
I finally got my head round the game rules while chatting with friends.
Pro Tip 2/3Emotional Acceptance
May also mean accepting something emotionally, not just understanding it intellectually. 
He's still trying to get his head round the fact that she left.
Pro Tip 3/3Time and Effort
Often implies that understanding took time and was not immediate. 
Janet got her head round the new procedures after a few weeks.