First, read all you can. Witchcraft deals with a term of magic, right? You'd probably think, so.
However in oder to truly be a witch, you must know what a witch is. Therefore, study as much as you, can.
Along with that, as Bryson said above. Many religions, that use magic, like wicca, for example, can be claimed as a witch.
Is it true? That is that person's choice. To me, i believe knowledge, respect, and understanding of a variety of things(rocks,religions,magic, spells, health, hurt, ect) and their beliefs make a witch.
If you want to be a witch, ask yourself the following.
* What is a witch?
*What do i already know
*What i hope to learn?
*Do you want to include any religions?
Next if so, read the, ''basics:expanded'' by Awaketoolong.
After that, take out some books.