As someone else already wrote : study, research and meditate (not mandatory, but usefull if you can do it). Look in older forum posts to find book titles to get started with what you want to learn, read the articles, and , again, older forum posts till you find what you're looking for.
study. that's the most important thing. couple quick facts about magick:
magick does not work the way you see in movies. magick is energy found in nature, spells are a way for us to harness this energy and focus it to bring change into our lives. since it's a part of nature, it cannot go against nature. invisibility, transformation and flight are some things that cannot be done.
magick has no colour, only intent. while classifying it "white" and "black" is easier than "positive" and "negative", nothing with magick is black and white. think long and hard before casting. many spells might seem straight forward but once you scratch the surface they're not.
anyone can cast spells, you don't have to be a witch/wizard/warlock/whatever.
magick isn't exclusive to one religion. magick is energy, while most include their spirituality in spellcasting, a spell can be cast without calling upon a higher being. it can also be cast calling upon any deity you feel connected with. [though some deities are better suited for certain spells]
there is no devil in the craft. Satan is a Christian concept. it's similar to saying to a Christian they're angering Kali, it's a different religion, and they do not believe in that particular goddess. same goes for Pagans, some follow Lucifer, but most do not believe in Satan.
if you want to become a wizard, it's just a title, so you can start calling yourself that if you want. if you are interested in a particular religion, i suggest studying it before converting. hearing that witches are real and they cast spells, doesn't mean you should instantly sign up. as i said above as well, you can cast spells and not convert. you could call yourself a wizard and still be Jewish. [or whatever religion you are] if you do wish to convert, you should study every day, for a year and a day [which is a common ceremony/ritual most Pagans go through before making the choice to become a witch] if you just want to cast spells, you should study, but you can skip all the religious elements with the God and Goddess and the holidays. though you should study"
energy work [charging/centering/grounding]
facts about real magick. what it can and can't do
basics on herbs/crystals/colour association
there is a lot of other things you could learn about and study, but you can choose for yourself as you go on. starting out, you should learn the basics. starting from step seven might be more fun than step one, but you'll be confused, and most likely upset when you find out the facts about magick. blessed be.