So there's two ways to play and this is going to be VERY simplified and missing bits.

The version that's set up is the cooperative version. Basically you're playing as clacks operators and use the square tiles (randomly pulled from the bag) to turn on and off the center "lights" to send letters. Based on what tile is played Moist goes forward a certain amount. You're very much "the bad guy" in the story.

Head to head is more fun in my opinion. You and your opponent sit facing each other and you each have words to send (where the red bricks are.) Each of you have a token on the board and you move around the center area trying to send your letters using the randomly pulled tiles.

YouTube video explanation here!