How it works is all over the forum. And if they don't understand after we explain it, not our problem.
A player can always go to the stable and check to see if pets are stored or not "before" getting / activating new ones2. Put the pets in there and some time passes by. You forget if your pets were killed or are stored, and you're able to get new pets (shop or otherwise). More time passses until you need to store those fine pets you've been wandering with for weeks. Uh oh! You're stuck!
I'm a guy that lost way to may pets to my own OOPS!
And today we even have a "Test Server" where we can test things.
Perfect place to test the Pet Companion with cheap Shop Pets and learn just how it works.