Nothing, you simply have a foreskin. There's nothing wrong with not being circumcised. The only problem that exists is circumcision. It's literally the mutilation of an infant's genitals because of unproven beliefs.
The purpose in the foreskin is to protect the sensitive tip of the shaft. The tip of the shaft is a section of sensitive meat. The foreskin protects that.
I remember when I was in elementary school and that skin would pull back sometimes, exposing the sensitive tip. It was extremely uncomfortable, that tip touching fabric. I don't know HOW circumcised men deal with that.