You must first equipt your ring by double-clicking on the item(tales of pirates II gold) or dragging the item to the spot in the equipment section of your inventory with the picture of a ring (preferably in a non-lag area for charge the ring, it's just tedious having lag when trying to equipt something). Then you must solo-battle either sea or land monsters.
You get full exp even when solo-training with the Star of Unity ring equipted, therefore you do not lose any exp when killing monsters. The ring does not charge when in a party no matter what the lvls of the characters are. In other words, the amount of experience stored in the Star of Unity will not increase when you gain exp in a party. The ring's exp can only deplete.
When training, the star of unity is charged according to how much exp you gain from the kill yet rounded down to the nearest tenth. Ex. say you received 1288 experience from a monster that you killed. The amount of charge that the Star of Unity ring will receive is 1280. If you have successfully charged your Star of Unity you can now use it to increase your experience gaining by 3x.
First of all you must be in a party with someone 5 or more levels lower than you. If you are level 30 the lower level character in your party must be level 24 or lower. If you're level 26 you need a party member at level 20. Just subtract 6 from your current level and find an appropriate party member. This is when the experience that is stored in your Star of Unity will cause the charge to deplete and the experience be given to you.
You do not need to be close to your party member to gain the 3x experience. You can simply party up with a player and head off to lvl solo. The 3x Experience can stack with Double Experience days and other items that can increase your experience gain. Just have fun in Tales-Of-Pirates-II.