Here's the breakdown:
* Dogs are domesticated wolves. They were selectively bred over thousands of years by humans from wild wolf populations.
* Wolves and dogs are still very closely related. They can even interbreed and produce fertile offspring.
* Therefore, you could say that wolves are ancestors to dogs, but not that dogs are descendants of wolves. They both share a common ancestor and evolved from that point.
Think of it like this: You and your cousin are both descended from your great-grandmother. You're not descended from your cousin, but you both share a common ancestor. The same goes for wolves and dogs.