This item gives a x2 xp bonus in any skill up to a total of 68,800 XP. To activate the bonus, right-click on the item and choose 'Gain xp'. You'll be asked which skill you'd like the bonus to go in. Choose your preferred skill and the bonus XP provided by this item will be added to your bonus XP pool.
Once the xp boost has been activated, the amulet will become cosmetic.