Summarize this article in one sentence.
Mix the egg whites at medium high or high speed with an electric mixer. Keep the mixer moving around the inside perimeter of the bowl so all the contents are mixed equally and thoroughly. Properly beaten egg whites will be uniformly white and will be rather stiff. They should also form soft peaks and be light and fluffy looking. This is a critical step. Some cookbooks recommend adding a small amount, usually less than 1/4 teaspoon, of Cream of Tartar to help with the beating. The cream helps make the egg whites fluffier. Gently mix this small amount of egg whites into the batter. Doing this is called ‘tempering’ the batter and helps with when mixing in the rest of the egg whites. Only stir the egg whites into the batter until the batter looks barely combined and slightly clumpy. Make sure all other ingredients are thoroughly mixed according to the recipe you are using before adding the egg whites.

Summary:
Place the egg white(s) in a straight sided mixing bowl. Beat the whites until they have the right consistency. Put about a third of the whipped egg white into the batter.