In Skyrim, the disease known as lycanthropy is responsible for turning people into werewolves.
Any player can decide to become a werewolf by joining the Dawnguard faction or completing The Companions questline. The Dawnguard DLC introduces a new tree for Werewolf Perks.
Option 1
Members of The Circle in Whiterun are actually werewolves, according to a secret shared among the Companions. Follow the questline to join the Companions until you reach the quest entitled The Silver Hand.
Here, you will be able to participate in a secret ritual that allows you to drink the blood of a werewolf to turn into one yourself. If you do not commit, the quest won’t advance. Keep in mind that the transformation is reversible using a cure.
After the outburst, you will acquire Beast Form, found in the Magic menu under the Powers section. Similar to all other Powers, Beast Form can be activated once per day.
Option 2
It is possible to turn into a werewolf by completing the quest Ill Met By Moonlight. Once you talk to and agree to help the prisoner in the Falkreath Jail, you will receive the Cursed Ring of Hircine which will not allow you to remove it until the completion of the quest.
Next, you’ll take on The Hunt quest, which brings you to Bloated Ma’ns Grotto. It is here that you will join a team of hunters to slay a great white elk that turns out to be an aspect of Hircine, the daedric lord.
This daedric lord will cleanse the ring if you agree to slay the thief that gave it to you. Conversely, you will have the option to slay the hunters and partner with the Werewolf as an NPC. If you finish the quest instead, you will receive the reward Savior’s Hide.