Puff pastry is a flaky, layered dough that is used for both sweet and savory dishes. It is related to Middle Eastern "phyllo" dough and was popularized in French cuisine in the 17th century. The dough is rolled into layers and then folded over to create the flaky crust. Pre- (or blind) baking a puff pastry can help keep the dough flaky when it is being used as a pie crust.
Press the puff pastry into a pie pan, trimming off any excess crust. Don't press the dough too firmly or your crust won't be as flaky.
Place the second pie pan into the first, on top of the crust. Fill the second pan with the dried beans, spread evenly. This weights the second pan so the pastry won't puff up excessively.
Preheat the oven to 450 F and bake for 15 minutes. Then fill your pre-baked crust with your filling of choice and finish baking as required by the filling.
You do not need to blind bake a puff pastry, but it can save time in the baking process as well as ensure that your crust stays flaky when you are using an especially wet filling.