It is very easy to play. Have him/her break off some of the play dough and make three balls. We made each one a different size. You could also play with more then one child and use a different color for each child.
Then I called out the letter,size it was and what size ball he should use. Beyond the fact it was a wonderful way to use his letter recognition and have his confidence grow that he knew his letters,it also was a great listening skills game. It held his interest for a long time. He also requested to play the game again. Which made me feel great. I am finding that he truly enjoys hands on learning like this.
Let me know what's going on in your learning space!