sort of a broad thing to ask, since Wicca, Witch, Pagan, and Witchcraft are all different things. [i sort of get what you mean though] Pagan [Paganism] is just the umbrella term for people who either practice magick, pray to multiple deities, or don't follow the Jewish/Christian/Islamic God. Wicca is a faith founded in the 50's by Gerald Gardner, based off old traditions, and has evolved into one of the most well known branches of Paganism. a Witch is someone who practices magick or lives by the God and Goddess but doesn't follow the teachings of Wicca. [though a Wiccan can call them self a Witch] Witchcraft is the artform. which one are you concerned with? i ask because i don't want to help you with Wiccan views, but you just want to cast spells and not actually follow a religion.
start with meditation, it's got a lot of health benefits, but it's also important with spell casting. energy work, circle casting, some basic knowledge of colours, herbs, and crystals wouldn't hurt, as well as some tools such as an Athame, and terms such as Esbat, Sabbat and Athame can come in handy. in terms of books, a basic beginners guide would be a good idea such as Wicca: a Guide for the Solitary practitioner by Scott Cunningham or Wicca fro Life by Raymond Buckland. while these books are for Wicca, it can help anyone when they begin their path.
also if you haven't already, you should speak with your parents, they're responsible for you until you're legally an adult, so you need to tell them. as well, Lark wrote a forum i feel you should read, as well as one listing reasons why you shouldn't join:
i don't mean to upset you with the above articles, but you should know why you want to practice magick or convert to a pagan path. if your reasons are fickle ones, things will end badly. mind you, there is nothing wrong with just casting spells without any religious affiliation, but this too takes consideration and understanding.