The first thing you need to know is that Hoodoo is not Voodoo. Hoodoo (or rootwork) is folk magic. As is the American tradition, our forefathers were from various backgrounds and cultures. As such, their cultures fused into an amalgam of beliefs and traditions. The same can be said of Hoodoo.
Hoodoo is African folkloric practices, European tradition, and Native American botanical knowledge. Most of the people who still practice Hoodoo live in the Southern US where a majority of them are Protestants. They use bible verses (particularly from the Book of Psalms) to strengthen their rootwork.
Not every rootworker is a Christian, though. Rootwork doesn't require prayers to Gods or a religious background. The practices have some steep traditions, but specifics vary between rootworkers. The differences come by what's available locally to the rootworker.
Ingredients for spells are typically things you can find in the average kitchen or can easily acquire and store in one. Where one cooks, one works (casts spells). Hoodoo is all about making a connection to supernatural forces via what is handy.
Some things that exist in most traditions of Hoodoo include Honey Jars, Candle Readings, Petitions, and Alcohol. Hoodoo can do a variety of works, from attracting a person, job opportunity, or spirit towards you or others, to crossing someone with heavy curses, hotfoot powder, and spiritual torment. There is no "black" and "white" magic in Hoodoo. No good and bad. There simple "is". The morality of magic doesn't exist the same way the morality of knife doesn't exist. It's what you do with it that makes a difference.
Most Hoodoo practitioners don't prescribe to the idea of karma or the three-folds law of Wiccans. Rootworkers don't think there's a cosmic justice system that will penalize them for crossing someone. But they understand that every action has a reaction, good or bad depending on the circumstances.
Rootworkers can work with spirits by use of gravedirt and other curios related to the spirits they want to work with.
If you have any further questions, feel free to ask.