You'll notice a new category under Darkwater's post in his berth. There is going to be sometimes a section added to posts called 'Pets'. It will appear when there is a creature one can tame or control. Pets can be all manner of things, to things one can summon to actual everyday pets. To keep a pet, however, one must bond with it. They can do this in any manner of ways, each way varying depending on the creature.
And yes, Bestiary creatures can be bonded with as well...