If you can't make a word from the cards that are currently on the board, you can use the face-up draw pile card, or tap on the draw pile to see additional cards. However, use the draw pile sparingly... you'll get a score bonus at the end of the level for any unused draw pile cards.

You can use the Undo button to "unflip" draw pile cards. You can also buy more draw pile cards if you run out. The cost in coins of these actions is shown on their respective buttons.