To 'wrap your head around' something means to finally understand or comprehend something that is difficult or challenging. This phrase can also be used to talk about accepting something that is contrary to your ordinary beliefs. This expression can also appear as 'to wrap your mind around'. This is a casual expression that can be used in social and professional contexts.

1. It has taken me a long time to come to terms with what happened, but I feel I'm slowly wrapping my head around it.

1. I know this is your first day here and there's a lot for you to wrap your head around, so just give me a shout if you need any help.
2. My interview couldn't have gone much better, so I just can't wrap my head around how I didn't get the job. I must be missing something.