Microsoft Access form help?

I'm creating a form to keep track of info for a bowling league I'm helping out with. I have text boxes for the 3 games each person bowls and one for the total of those 3 games. What will I need to do in order for the Total text box to automatically total the 1st Game, 2nd Game, and 3rd Game text boxes? Is it a validation rule or do I need to do something like this in the actual code & what would it look like?