First of all you need to examine 'why' you want to be a witch?You need to search deeply first of all and ensure that it is the path you want to follow. Most schools will ask you to write down why you want to do this.
Most witches actually go under the name of Wicca/Wiccan. For obvious reasons this has less of a negative tinge about it, since most people today still see Satan worship and Witchcraft as the same thing, which of course it is not. For a start Wiccans don't believe in the devil.
It also depends on what kind of Wicca you want to be invovled with? Do you want to belong to a group? Do you want to be a solitary practioner? Do you want to study with a tutor face to face or remotely?
The majority of the study to become a Wiccan is learning about yourself through meditation and other excercises given by your tutor. Learning about the Goddess and God, history, folklore and many other subjects. But it depends on your tutor and their teaching methods. Wiccans also have an excellent philosophy that they advise you to work and live with - 'do what though will as long as it harms none' - this includes yourself and any animal or other part of nature.
It might at first be very useful to search out a couple of information books from say Amazon, E-bay or other on-line book sources. Put in a search for example 'learn wicca', 'all about Wicca' and so on. These will give you more in-depth information and 'good' sources of tutoring. It is important that you get a school/tutor who is very experienced in Wicca and is dedicated to your instruction not just taking your money. It is possible to study on-line/via e-mail, at least for the novice levels of Wicca. If you feel you have found a tutor, investigate first. Ensure that you can withdraw from enrollment if it is not for you. One of the best organisations to keep you on the straight and narrow is the Pagan Association who have lots of free information. If you are in USA or Canada they will have the equivalent association.
Lastly, look up some of the Pagan hubs on Hub Pages, there is bound to be some excellent advise - and more knowledgeable than me - to get you on the right road of light!
Hope this has helped - lots of luck!