Press "H" during game play to reveal tile matches.
Better Win Percentage:
If your win percentage on a certain board is low, reset and play on that board until you play a game you know you are about to win. When you have only a few matches left, exit the game. It will prompt you to save, so save. Then load up the game again. Match the remaining tiles and click through to the win screen where you see your high score and your win percentage. Exit out of the game. Load the game back up. If done correctly, you should be prompted to load up the game you just won. Repeat as many times as you want to give yourself a high win percentage on the high scores board.