Conjuration is the art of materializing objects and summoning beings at will. This power is generally possessed by Witches and Warlocks. According to Miranda, only the most powerful Witches can transport human beings. To conjure an object, a witch or warlock has to focus and concentrate on what they want to conjure.
There are rules about conjuration. A witch or warlock can't conjure anything they want. If it's for the greater good, then it'll be okay and if it's for their own benefit, it has to be within reason. If they do it too much, then they will be called in it by Wicca society.