Baking soda and baking powder are not the same thing. Baking soda is bicarbonate of soda and is basic, which means its pH is higher than 7. Baking powder has bicarbonate of soda as well as acid salts such as cream of tartar or starch. Baking powder is generally neutral.
Both baking powder and baking soda are considered leaveners, which means they create carbon dioxide that helps dough or batter to rise.
Baking powder can also be single or double acting. Double-acting baking powder reacts both when it's being mixed with the dough or batter and again when it's in the oven.