Be the first to play away all of your domino tiles. sometimes you won't be able to play a tile, and then all of your tiles will turn red. In that case, click on the deck to draw a new tile until you can continue.
Use the mouse. Click on the deck or on the tile you would like to play. If a tile can be played on both sides, click on the left side of the tile to place it left and on the right side to place it right.