Sims can have fun with pets, build relationships with them, and enjoy socializing with their companion animals. This should help newer players to understand how to take care of a pet and the realities of owning one. I say that as a pure gameplay guide writer, because it's not exactly easy to write about how owning pets works in terms of gameplay. Owning a cat or dog in the Sims 4 Cats and Dogs Expansion doesn't add major gameplay changes mechanics-wise, they're just a great household addition.
The Sims 4 Cats and Dogs Adopting, Training, and Caring for Pets