Click the button to begin playing. You can pause the game at any time with the same button. It will pause automatically if nothing happens for a while.
You will hear a word. Click on the word you hear to make it disappear. You can listen again to the last word by clicking the replay button.
You can make the words (on average) easier or harder by changing the level. This cannot be done when a game is in progress, but you can pause the game and change the level to get a new grid at a different level.
You can make the word grid larger/smaller by clicking on the grid button.