Circumcision is where the skin that covers the end of the Penis is removed.  This is a simple operation and it is offered to boys or men if their foreskin is too tight to pull back easily, and this causes it to tear or burst when they have Sex.  The benefits are that it is easier to keep clean and prevent build up of smegma under the foreskin.  It also leads to fewer Infections including HIV.  Some religions and cultures circumcise all male children at birth.