While fighting monsters and acquiring experience points, an additional equal amount of XP is stored in the amulet until its maximum capacity is reached. (When the amulet is full, you can right click on it to exchange it for an Experience Orb. Cannot be removed once equipped, equipping a similar item will replace it making it disappear as a consequence of this.)
Convert , when filled, into an Experience Orb, then use it to increase your XP. The Experience Orb is NOT bound and can be traded, sold, or mailed to an alt.