Vitamins are needed in small amounts by the body to regulate chemical reactions within the body. Each vitamin has a specific significance to your body. There are 13 known vitamins, five of which your body makes itself. Biotin, vitamin K, niacin, and pantothenic acid are four of those five (honestly, I don't know the fifth, please fill out the feedback form below if you happen to know what it is). These four are produced by bacteria which live in your body, and are produced in sufficient enough amounts that you may not need to take them in through your diet. Water soluble vitamins are vitamins that can probably be consumed in larger amounts safely. Fat soluble vitamins can be dangerous if consumed in large amounts.
Note: There are eight B vitamins, sometimes they are labeled with a number written in subscript (e.g. Vitamin B12), and sometimes they are named (e.g. Cyanocobalamin).