Begin this quest by talking to Pikkupstix in Taverley.
After he gives a brief explanation about the basics of summoning and you hear a crash upstairs, you will tell him that you'll take care of the problem. Climb up the nearby ladder and you will realize that the creature is not a cute fluffy bunny. After the cutscene, talk to Pikkupstix again and he will explain that what you saw was a wolpertinger and can be banished by a spirit wolf's howl. He wants you to create the pouch and banish the creature while he ensures it doesn't escape.
Talk to Pikkupstix again with two wolf bones in your inventory. If you don't have any wolf bones, go west of Taverley to White Wolf Mountain and kill two level 25 White wolves there for their bones. He will give you the following items:
Using the Trapdoor key, open the trapdoor located in Pikkupstix's house and proceed to the basement. Once inside, infuse two Spirit wolf pouches by selecting the infuse-pouch option on the obelisk. Once you have two pouches, use one of the Spirit wolf pouches on the obelisk to open the Transform Scrolls tab to create 10 Howl scrolls using 1 of the pouches.
WARNING: Using your second Spirit wolf pouch to create an additional 10 Howl scrolls will prevent you from proceeding unless you can acquire a Spirit wolf pouch in another way such as by trading other players. If you are an ironman player, there is no other way to acquire a Spirit wolf pouch and you will be unable to complete this quest without starting a new character.
Once you have your Spirit wolf pouch and 10 Howl scrolls, return upstairs and talk to Pikkupstix with them in your inventory. He will tell you to proceed with banishing the wolpertinger. Climb the nearby ladder and after the brief cutscene summon the Spirit wolf by right clicking on the pouch in your inventory. Once summoned, click the Howl special attack icon and cast it twice on the Giant wolpertinger (the first time progresses the cutscene, the second one banishes it). Once the wolpertinger has been successfully banished, you will automatically head back downstairs.
Talk to Pikkupstix to inform him of what happened, and he will tell you to replenish your summoning points. Head back to the basement and replenish your summoning points by select the Renew-points option on the obelisk. Once your points are restored, head back upstairs and talk to Pikkupstix to complete the quest.