In theory everyone should vote but that'll never happen.
I think I read that in one country if you don't vote you get fined. I was right and there are more.
Australia has compulsory voting, and people are fined if they don't attend a voting booth on Election Day. If you are on the electoral roll you must get your name checked off - what you do with your vote is up to you. I think the fine is about $50 (Aussie).