When there is a proposal to vote on, you call the "vote" function from your wallet with the proposal ID and whether you are voting for or against it.
You don't have to vote on a proposal to get any rewards from it. If you have tokens when the proposal is passed and executed, you are invested in that proposal proportional to your share of the total existing tokens.
Your tokens are yours forever, unless you burn them in a split or trade them on an exchange. You're not really "using" them to vote, the contract is just checking your balance and using that to assign a weight to your vote. If you have 1000 tokens but you only want to vote with 100 weight, send 100 to another address and vote with that address.. but I'm not sure why (unless you're hedging some tokens for a possible split) you'd want to vote with less than your full balance.