Wicca is centered around the use of positive thought, positive action and love of nature to create an atmosphere of positive energies which are then used for our own benfits. Wicca teaches that there is much more in our universe than we can see or understand. The central law of Wicca is: " An It Harm None, Do What Ye Will" which means exactly what it says: as long as you don't do anything that will hurt anyone (including yourself) it is allowed. This rule is reinforced by a second major aspect of Wicca: Everything you put out comes back to you Three fold. This means that every good deed you do, every terrible thing you do, every good spell you cast, every harmful spell you cast will come back to you thrice what you put out. Therefore, the punishment for breaking the law of Harm None is a threefold return of whatever you did.
The difference between Witchcraft and Wicca is, for many, a fine line. I think the two are best differentiated by the idea of religion vs. practice. And it is important to note: there is NO DEVIL in the Craft.