Hunters are directed by their trainers to speak to Gytha Lainey at Adso's Camp in order to complete their epic class quests. The first quest is at level 15.

Adso's Camp is "on the Great East Road between Bree and Buckland" as relayed by the quest directions. That road is on the west side of Bree and it takes you directly to the camp about a quarter to a third of the way to Bree. There you'll talk to Gytha Lainey who has doubts about your prowess as a hunter and suggests putting you to the test. That test being a solo battle between you and the wolf, Yellowfang.

If you haven't already done so, it might be worth it to pick up a few helpful skills for this quest:

Cry of the Predator - a 'fear' skill
Passage of Nature - a tracking skill
Set Trap - traps to hold an enemy temporarily

The quest is in a private instance. No fellowship is allowed, as this is a test of your ability as a hunter to take down the beast yourself.

Once inside, you'll find there are a good number of lesser wolves scurrying about. Using tracking, you can lock onto Yellowfang. He will appear as a red dot on your radar. Killing the lesser wolves before going for Yellowfang will reduce the chance of "buddies" joining him in his battle against you. It's also a decent source of hides and loot. Once you fight Yellowfang, it should be a pretty even battle. If not, remember that you can buy some time and "breathing room" with Cry of the Predator.

Once Yellowfang is dead, speak to Gytha again, and she will take you back to Adso's camp and give you your reward - some potions, a class trait, and a bear helm named Avornhar