Do not buy ordinary every day ceramic figurines that you can buy in any store. This can be very dangerous. There are certain chemicals in the paint used on them, such as lead, that can kill your fish instantly. Aquarium decorations can be more expensive, but better than losing an entire tank of fish. The simple ones, though, are pretty cheap whereas the elaborate larger ones run into a lot of money.
Many fish like to get inside of things and hang out.
I have a castle and a few other things in some of my tanks. Some of my fish love to get in there and kind of hang out. The decorations can be great places for a fish to run and hide if they happen to be getting chased by other fish. Decorations can also add to the beauty of your tank. There are even some that you can hook an air tube to and water bubbles come out of them.