Levening is what we do make dough rise and become much less dense. This actually involves somehow incorporating air into the mixture. Yeast, baking soda, baking powder and egg whites are the four most common mechanisms for levening dough. The secret is to cause a chemical reaction in the dough that will result in the creation of carbon dioxide.
Baking soda, or sodium bicarbonate, reacts with the acid in a dough to produce the gas. Typically, buttermilk, vinegar, or lemon juice provide the acid.
Baking powder, however, carries its own acid with it, thus avoiding unwanted flavors.
Here are several baking recipes Jerry has used at Schola Cooking School.