black magic is usually involved with negative energies so its more fighting fire with fire. i wouldnt use it as a protection thing. white magick will protect you very well and it will sometimes filter through energy and make them pure again. a energy sheild is usually used for protection. when you mean "teach them a lesson" i think you mean the return to sender spell. thats not considered black magic unless its targeted towards a very specific person that you know of. the return to sender spell is casted to reflect a spell, you DONT KNOW THAT PERSON. thats the beauty of white magic.
Gwen your best bet would be to find a coven and look for people to guide you. You are always able to ask for advice and suggestions in the public chatter and forums, and joining a coven will only add to your resources. Just bear in mind that experience is the best teacher.
I would not agree with anyone who believes that you need black magic to protect your self.
As 2396022 said, it is like fighting fire with fire. White magic is used for protection mainly, as well as healing and personal gain without harming anyone against their will.
Black magic is used mainly to cause what white magic does not, brake of free will, harm and negative energies.
With a few words, your karma will be suffering.
However, there is a difference between knowing and practising. I for example have no problem reading black magic (Although I do not usually do) but I would never practise it on somebody as I am practising white magic.