To be fetching is to be attractive and beautitful. A fetching woman catches people's interest.
When a dog fetches something, he grabs it, just like attractive sights take your interest. Fetching is a word for sights that capture your interest because of their beauty. Usually, this word applies to females: you're most likely to read about a lovely, fetching woman. A beautiful woman who everyone looks at is fetching: she grabs their attention. You could also say other things, like a gorgeous mountain or a well-designed building, are fetching if they grab your attention.