Some recipes call for just egg whites or just egg yolks. How do you separate them? You could use an egg separator, but it's really not too tricky to just use the shells.

Set yourself up with two bowls -- one for the whites, and one for the yolks.

Carefully crack the egg on the edge of your bowl. Holding it over the bowl you intend to use for the whites, turn it vertically while you separate the halves, so that the yolk sits in one side of the shell.  Some of the whites will spill over and into the bowl.

Gently pour the yolk back and forth between the halves, keeping the shells tilted so that the rest of the white can drip over and into the bowl. Once most of it is gone, dump the yolk into the other bowl, discard the shells and repeat. It takes a little getting used to, but a few eggs into your angel food cake, and you'll be a master.