Incoming 1st year - difference summer/winter hiring for clubs?

I'm a bit confused between the summer/winter hiring sessions. For example, a club I wanted to join had hiring around May (summer session) then October (winter session). Is the summer session to become executive for term 1 and winter term 2? Can I apply for this club in the summer hiring session, and then re-apply in the next round if I get rejected? As an international student, could someone explain how club hiring works?