If you put Hircine's ring on, you will turn into a werewolf for around six hours. You won't suffer from bloodlust, so you won't lose health if you don't kill anyone. But if you put it on while NPCs are looking, the world will still know you as a werewolf.
This ring has an enchant value of 120 like exquisite rings do and can contain spells without messing up the werewolf ability. When you are asked if you want to turn into a werewolf, select no, and the ring will grant the enchantment instead.
Tharsten claims that he has worn the ring for many generations, implying that it lengthens the wearer's lifespan in addition to its more obvious properties.