If you're new to the pet-owning experience, it's a good idea to try out a virtual pet first. That way, you can get used to taking care of something without any real commitment.
These apps are just like the Tamagotchi toys that were so popular in the '90s. You have to feed and clean up after your pet, and make sure they don't get sick or hurt themselves. If they do (or if they die), you'll have to start over with another one.