Photo: drewsaunders, Flickr
Parchment's most obvious use is to prevent cookies and cakes from sticking to pans -- cut a piece to fit the bottom of your baking dish, lay it down, and watch cookies slide right off once they're cool.
You can also use it to cook fish or chicken en papillote; which literally translates to "in parchment." Place a fish fillet with a little white wine, salt and pepper in the center of a heart-shaped piece of parchment. Fold the parchment over; then, working from one corner, crimp and fold until you have half-moon shaped packet. Place on a cookie sheet and bake until done.
You can also use parchment to cover a simmering dish on the stovetop to prevent moisture from escaping.