I don't think I need to explain what a healing spell is used for. I will, however, give 2 warnings.
1) Never use magickal healing instead of medical treatment. The magickal healing techniques are used as an aid to the medical process, and you should always recommend that the patient see a qualified professional.
2) Never perform a healing spell on someone without their express permission. This has the same reasoning behind it as why you should not cast a love spell on a particular person. This, of course, is up to your judgement, but I have found that most people, if trully ill, will be willing to 'try anything' to get better.