Parchment paper has a myriad of uses in the oven: Use it to line baking trays to make cookie removal easy; protect pie crust as you bake; wrap vegetables and fish or another protein en papillote -- a folded pouch; or place it in the bottom of cake pans for easy release. It's oven proof, but not completely impervious to heat. It may burn at high temperatures used for broiling or baking pizza, for example.
Parchment has a nonstick coating that works for just about any baked good. It prevents the dough or batter from coming in contact with the metal baking pan and thus slows browning. Sugar cookies, for instance, baked on parchment don't burn around the edges as readily.
Cleaning up with parchment is easy, too. Discard the paper after baking, and the pan is essentially clean. There is no greasy, filmy surface to wash.
When you use parchment paper to line cake pans for easy release, put a little grease or cooking spray underneath it. This helps the paper stick to the pan so that batter doesn't seep between the paper and pan, ruining the surface of your cake.
Parchment is made of cellulose, a plant matter. Sheets of the plant pulp go through a bath of sulfuric acid, which partially dissolves the paper and imparts a nonstick property to it. Paper may also be coated with a silicone mixture that makes for easy releasing.
Parchment paper doesn't have a "side." You can flip it either way and it will work the same.
When used at baking temperatures below 400 F, the paper may brown -- but it shouldn't burn. You can even reuse parchment paper several times, but once it becomes brittle and much deeper in color, it's past its prime and should be discarded. If you use parchment at a temperature close to its maximum and add grease to it, it may burn more easily, as the grease will heat more quickly and exceed the paper's temperature limits.