
"Who's going to carry all this loot?!"
Pets & Companions are things that you acquire in-play, whether you find them, buy them, or earn them as quest rewards. Some pets are basic and do not have much to offer besides a cute friend. Others, are more capable of joining you in combat (though, death is permanent for the little fella!). Then you have some that are capable of being your pack animals, carrying the load that you can't, so you can make it somewhere safe!
When you have the acquired "Pet Token" (which cannot be set down), you will be able to have the pet follow you, or wait somewhere for you, though they never completely despawn unless you log off. If the creature has a pack of sorts, anyone is able to look at the creature's pack, so remember to keep dirty grubby hands away from your loot!
Otherwise, you can use the Associate Control widget to move them around, command them to attack, etc.. You can also emote through them, and in some cases, speak, using the !v command.
Do not leave them locked up in storage units, small buildings, caves, or other places alone, they will start to smash furniture, and other things in retaliation if left to wait in such confined places. It is perfectly safe to have them follow you into those locations as long as they are still set on "Follow" mode not "Wait" mode.