The phrase "over one's head" means to be too difficult or complex for someone to understand, handle or manage. It can also mean that something is happening around you that you don't fully comprehend or are not equipped to deal with.
You can easily get in over your head in such a short while. (moneywehave.com)
These policies guarantee food on the table and a roof over the heads of the family. (lifeinsurancehub.org)
The gags in the hotel room over his medications when the doctor is called is very good, and possibly goes way over the head of younger audiences. (timeout.com)