After slaying 8 Flatland White Apes, return to Master Zhao to receive your reward and your next quest, "First Pet".
Master Zhao (160,157) instructs you to head towards eastern Da Li to speak with the pet vendor, Lily White (265,129). Lily will give you a quest called, "Level Up Pet" that requires you to head back to the Wild Plains or go to Mt. Infinity to familiarize yourself with the pet system in TLBB. Once you’re in Wild Plains or Mt. Infinity, open your pet window (Alt+X) and select the "summon" command. Now that your pet has been summoned, you’ll notice that whenever you attack an enemy, your pet will attack it as well. Your pet’s health and experience are displayed under your own, so make sure you keep a close watch on its health.
When you’ve defeated enough enemies to get the pet to level 2, return to Lily White (265,129). She will send you to Master Zhao (160,157) so that you can receive yet another recommendation notice. Now you can keep that pet to fight with you till level 10 or free it as well.