People with no occult knowledge tend to blur the practices of voodoo and witchcraft together, not really understanding that they are very different things.
We already talk a lot about witchcraft here since it is the main topic of this site. But in a nutshell, it is a magickal practice that is not tied to any particular religion or faith system. Though the term can be used for many different types of magick around the world, the kind of witchcraft we are basically covering here is a British / European style. It uses the natural energies within us and within natural elements such as herbs and crystals to make changes in the world.
The fundamental difference between voodoo and witchcraft is the spiritual aspect. As I said, witchcraft is only a practice but Voodoo is a true religion. Their practices revolve around specific beliefs and a pantheon of Gods and Goddesses. The main creator spirit is called Olodumare and the rest of the Deities are known as loas (or lwas) and they are considered to be aspects of this greater spirit. For most people, it's just easier to think of them as Gods or Goddesses.
Voodoo has its origins in western Africa and is a common faith in Nigeria, Benin and Togo. Through the slave trade, it came to the Caribbean and is a common religion in Haiti and Cuba today.
Spellwork is part of Voodoo, and my page of Voodoo spells can show you some good examples of them. Rituals are usually more aggressive than witchcraft, and though spells can be cast by individuals, most rituals for the religion are performed in groups. They are very active rituals and can involve animal sacrifice as well as spiritual possession.
Really, there are many things that make voodoo and witchcraft different, and they can't be easily summed in just a few bullet points. The main point is that Voodoo is a religion whereas witchcraft is not. They have their own set of beliefs, practices and rituals and though they may seem to overlap in some ways, they are very distinct from each other.