Baking Soda, well known as bicarbonate soda. It is a alkaline compound , usually sodium bicarbonate. It neutralise acids in dough or batter. This encourage batter to rise in the oven. The bi-products of this reaction are water and carbon dioxide. It is usually used along with baking powder in cakes with acidic ingredient like sour cream, honey, molasses, fruit and buttermilk. It also encourage browning.
Cream of Tartar is an acidic salt, potassium bitartrate. It's role is to stabilise beaten egg white and improve the texture of egg-foam cakes.
Baking Powder has a mixture of chemicals that react to tied carbon dioxide when liquid is introduced. It consist of an acid salt, an alkali, and a filler, usually cornstarch, to absorb moisture and prevent the compounds from reacting in the jar.