Witchcraft or wicca is a pagan religion--a religion of nature.
The first step to learn witchcraft is to study the religion itself.
You can do this by studying as many books and journals both offline and online. This will enable you to understand the basic tenets and beliefs of the witchcraft. Since witchcraft is the religion of nature, it would do you much good to directly go into the lap of nature to experience its feel, to read books from brooks and sermons in stones. Watch the flight of birds through the glorious sunrises and sunsets across the mountains and seas. Look with wonder at the earth and sky, which are the bodies of the God and Goddess. Now take a notebook and write down why you want to become a witch. How do you visualize the God and Goddess? Be honest. Later on this notebook shall become your Book of Shadows.
The next step is to explore the magic.
Magic is not a hocus pocus way of bending the laws of nature to suit your needs. The magic of the witchcraft is to raise and channel energy that is within you to bring it in harmony with the nature to achieve the desired result.
For this you need to understand the fundamental principles of
Try to understand the various phases of the moon, its waxing, growing full and waning and their effect on your moods and body.
You must also do some meditation and visualization exercises to increase your concentration and focus. Learn to derive strength from the earth, sun, moon and stars. Learn to be still, calm and quiet and hear the voice of God and Goddess when they call you.
Now you can begin your basic spell work starting with your new moon ritual.
Do not go after the word-for-word rituals that you read everywhere. These are only the guidelines. Write down your own rituals. Having done that you should dedicate yourself to the Witchcraft. Then you may join some coven or network of your fellow Wiccans. You must be particular about the ethical aspect of performing witchcraft. If you try to harm someone with your magical powers, you will face the results of your ill intended actions very soon.