Fluting or crimping refers to the decorative shaping of the edge of a single crust pie. Double crust pies are generally crimped to seal the bottom and top crusts together as well as create a decorative pattern. This is done using a fork and pressing around the edge of the pie to seal the crusts.
To crimp a single crust pie, gently press a finger along the inside edge of the pastry and use the index finger and thumb of the other hand to to press the pastry around the finger. Do this around the entire pie.
(Photo courtesy of Better Homes and Gardens)