It's pretty easy. Open your wallet, and there should be a tab next to "transactions" called "votes." Click on "Votes" and choose a delegate that you want to vote for. It will cost you one Ark to vote and 1 Ark to unvote and 1 more to revote. However, you can easily make up that 1 Ark in no time if you have the right delegate and payout.
RE: Is it a good time to buy in?