Few animal lovers have an empty home with no pets. So it’s more likely that when you adopt a cat, you’ll need to acquaint your cat with your existing pets such as a dog or another cat. (Cats have no problem meeting any fish or rodents you might own because they’ll see it as a snack rather than a fellow housemate.)
Since animals can be territorial, you may need to get both animals to associate each other’s company with something pleasant like food or treats. The more you get your pets to associate the other with something enjoyable, the more likely all your pets will get along.
Be sure to shower affection on your existing pets while making the newcomer feel welcome too. The process of introducing a new cat to a home can go smoothly or go terribly wrong, so put the odds in your favor and do what you can to make your cat happy.