A simple experience chest. Best used if you are a high level and don't want to take a chance at losing your experience when you go adventuring. Also good if you just want so save up your experience without having the risk of one of those pesky creepers kill you while you are just getting a few resources. Now with an Ender Exp Chest you can store experience like the Ender Chest stores items. This means you can access your stored experience in any Ender Exp Chest from anywhere. The way the storage system works is exactly like the way getting experience levels in the game works, it isn't linear. So if you store 4 levels and then get to level 22 and try to retrieve those 4 levels your new level won't be 26 it will be somewhere between 22 and 26. This is because the amount of experience it takes to get to level 4 is less than the amount it takes to get to level 26 from level 22.