As the Creative competitions are shown from the main stage this evening, you are sure to have favourites among the entries. You may even hope that some of the best ones win something. And guess what - you can actually very directly influence the outcome of all the Creative competitions!
Note that it looks like it is possible to vote for the same entry for all three places. However, if you do this, only the first place vote will be saved. So don't do this unless you want to waste your 2nd place and 3rd place votes :)
Go to compo.tg12.gathering.org and login with your GeekEvents (or Wannabe, if you're part of the crew) account. Then you can cast your votes for best entry in each category. Voting will open right after the compo show tonight.
Once you are logged in, you click the next-to-last link to the left, the one named Vote. Here you will see a list of all the compos that are open for voting. Click the compo you want to vote in.
When you go to a voting page, there will be screenshots of the entries for that compo. Decide on your favorite three entries, and scroll the page until you see their screenshot and title. You can rank the three entries as first place, second place and third place. Your first place vote will receive three points, second place receives two points, third place receives one point.