From the manual:
The ToAd is a Role Playing Game. This means that there is a big story at hand and you are controlling the destiny of a character in it. You don't actually have to act or pronounce the character's lines if you don't want to. However, you will need to let everyone know the difference between what you are saying and what your character is saying. Try tacking a "Shamrock says," onto the front of whatever she says when it feels necessary.
You also have to let Shamrock be Shamrock. If you know that the Earth circles the Sun while Shamrock believes that it rides across the sky on the back of a giant dragon then you have to play by her world not yours. In the adventure there will be challenges and intrigue and mystery and wonder. Mostly though there will be lots of combat.
The Player's Handbook (4th Edition) contains the entire game rules; this manual is analogous to the ToAD: Tales of Adventure (1st Edition) manual in scope.