Voodoo is a faith that is a combination of Roman Catholicism and the tribal spiritualism of West Africa. When the slaves (primarily in Haiti) were taught Christianity, it blended with their own spiritualism and became what's known as voodoo. While a complicated faith to an outsider, voodoo can be learned and understood. Additionally, the inherent magic of voodoo can also be performed if a person learns it.
How to Learn Voodoo Magic
Learn about voodoo as a religion and faith. Voodoo is a religion first and a form of magic second. One cannot practice the magic until they learn about the spirits, called the Loa, who grant this power and aid.
Find an experienced teacher, if possible. Voodoo is like any other faith; you can read all the books that you want, but in the end you should speak with other practitioners about it to learn from their experience.
Design a ritual. Voodoo, like any other faith, is symbolic. However, that doesn't mean that voodoo spells are created like a recipe. There isn't a "speak these words, perform this action" sort of formula to voodoo magic. Rituals represent a spell, and they should be unique to each person. For instance, a love spell could call out to a certain Loa for help, and while you speak a poem that you wrote yourself, you could light red candles to represent love and power. You could also keep a photograph of the person you love on the altar as you ask for the Loa's help. Each "spell" should be unique, and crafted to the needs of the caster and the unique situation they need help in.
Be realistic in your expectations. Voodoo won't be a quick fix to your problems if you aren't willing to solve them from a spiritual and a reality-based perspective.
Avoid internet sites or mass media books that claim they can teach "voodoo spells" that will make you rich, powerful and attractive. At best these spells are fluff, and at worst they could make you seem like an unbeliever, ruining your chances of getting actual help.