Buy and install The Sims 4: Cats & Dogs expansion pack
Open The Sims 4 and create or load a household
Use Create-a-Sim to add a cat or dog to your household
Adopt a pet through a computer, phone, or adoption service in-game
Visit a pet adoption event if available in your save
Use cheats or mods if you want to add pets faster
Make sure your game is updated and the pack is enabled
If you want other animals, check whether they are included in the pack or require mods