How can a black female like myself grow longer hair?

okay..ive been feeling really frustrated lately for the simple fact that my hair is a centimeter past my shoulders but i want it touchin my back.ive seen many videos and things of that nature discussing and trying to teach you how to do that but its sooooo confusing!one lady says do this and that and another one says do such and such.can you teach me step by step?im 12 and im tired of my friends making fun of my hair length and im tired of wearin itchy braids all the time.thnx soo much:)