Join the Companions in Whiterun
Complete the early Companions quests until you are invited to the Underforge
Attend the ritual with Aela the Huntress, Skjor, and Kodlak Whitemane
Drink the blood from the ritual bowl
Transform into a werewolf during the ceremony
If you cure lycanthropy later, ask Aela for another chance to regain it during the Companions questline
In Dawnguard, become a werewolf again through Aela if you already had the power before curing it