The lofty pillow-like quality of meringue is the result of whipping egg whites into a shape-holding foam, adding sugar (usually confectioners or powdered sugar), and baking it. Some meringues are baked lightly, so their insides are still soft, others are baked until they are crisp all the way through. Most meringues are baked at a very low temperature to keep the egg whites from browning, but when meringue is used as a topping for other desserts (think Lemon Meringue Pie or Baked Alaska), it is put in a hot oven or even under a broiler to brown it quickly without heating up the rest of the dessert.
This basic method for making meringue shows you the technique for making meringue in a general way, whether large rafts of the stuff for pavlovas (I'm partial to this Rhubarb Pavlova), small buttons like those pictured above (or like these Chocolate Pecan Meringue Cookies), the poached "eggs" for the classic Oeufs a la Neige, the base for confections like homemade marshmallows, or meringue-as-frosting for pies and cakes.
Looking for exact amounts? For plain meringue, whether a single large raft, two 8-inch circles or two dozen smaller buttons, use 4 egg whites, 1/8 tsp. salt, 1/8 tsp. cream of tartar (optional, but helps the eggs whip up), and 1 cup powdered sugar; for one towering pie's worth of frosting-style meringue, use 6 egg whites, 1/8 tsp. salt, 1/8 tsp. cream of tartar (optional, but helps the eggs whip up), and 1/3 cup powdered sugar.