Prebaking, or blind baking, means to bake a crust before filling it. The technique is often used with single-crust pies. It is useful when the filling doesn't need to bake as long as the crust or would make an unbaked crust soggy. Some recipes have you partially bake the crust, while others call for it to be completely baked.
A foil ring can be used to shield the pie rim if it darkens too quickly. To make a ring, press foil into an empty pie plate to shape; trim outer edge, and cut out center, making a ring that's about 2 inches wide. Bake as indicated in the recipe. Let cool completely before filling, otherwise you could end up cooking some of the filling.