The base game, and every expansion pack, all come with at least one new Gnome. They mostly just do funny, comical stuff and wander around the house. Though they can sometimes cause trouble. As for how you get one, for the basic gnome, I believe you can find them while fishing, and when you send metals or gems to be smelted or cut, you sometimes get a gnome instead. You can also find them while digging through other sims' trash. When the Generations expansion came out, it allowed for Gnomes to basicly have kids and grow old and die. A WA gnome is a gnome from one of the World Adventure travel destinations. Each of the three countries has a unique gnome.