Where do you start? Researching, studying, learning. A really good post here is under General Info in the Forums, and it is called the Basics; Explanded.
How do you find an element that suits you? Understand that we are made up of all the elements, and you don't really "have" one. You can, and prabably do favor one more, but I would suggest trying to stay balanced in that respect.
How do you decide between black and white magic? There is no such thing. Black and white just symbolize the person's intent (whether it is good or bad) and it is really up to interpretation. Magic itself is colourless.