One of the shops in the Neopian Bazaar is the Grooming Parlour. Go there to get items for grooming your pet.
You can also get grooming items from some quests (see Jhudora), games or other activities (go to the Shenkuu Lunar Temple). Use the items to groom your pet (comb its mane, polish its teeth or use some mouthwash etc.) to make your pet look its best and feel better. This increases your pet's happiness.
Air Faeries will ask for grooming items to complete their quests, granting one of your pets 2 Agility points.