Anyone can call themselves Wiccan. Be cautious around people who claim to be Wiccan until you know them well enough to trust them. Most of the Wiccans I've met are nice people. However, in any large group of people, there's bound to be a few bad apples. Don't assume that everyone who calls themself Wiccan really is, or that they follow the Wiccan ethics code.
The main law of Wicca is the Wiccan Rede:
The Rede is basically stating that it is wrong to harm anyone. That is why you won't find a Wiccan who does manipulative magic (magic done for a specific individual without that person's knowledge and consent). Manipulative magic--even so-called "white magic"--is considered harmful, because it interferes with another person's free will. Occasionally, the point will be stretched in the case of a healing. But the main reason most people, teenaged girls especially, want into the Craft (which is not the same as Wicca, which I will explain in a minute) is because they saw the movie The Craft and want to cast a love-spell on some guy to make him want her. This is a no-no. So are curses; and that brings me to my next law of Wicca (actually, of all life in general).
See why a curse wouldn't be a good idea? It would have a boomerang effect. Trust me, manipulative magic is not a good idea.
So okay, you say, teach me about magic. Well, all right--but don't expect to be able to turn anyone into a frog. It just doesn't happen.
Magic is the alteration of natural forces, natural energy, that results in a change taking place. Magic is subtle; no Hollywood special effects. No glowing wraiths will appear in your living room during your first spell. Magic will simply alter your life in quiet ways. There are some ways of using magic that aren't quite so subtle, such as weather magic, but that is not something that a beginner should get into. Magic is like electricity: it can be incredibly helpful, or it can be dangerous.
For helpful uses, magic can be used to bring about positive changes in your life, such as increased income (don't expect diamonds falling into your lap; that doesn't happen either), or to heal someone (yourself included), or to bring love into someone's life. Oftentimes a spell may ask for what is best for the person it's for, rather than naming a specific goal. You know the phrase, "Watch what you wish for--you just might get it"? It's something to keep in mind when dealing with magic.