This is your inventory.
Everytime you or someone else visits this page (your inventory), your XP will be updated, and so you can only level up by visiting this page.
This is an item:
It has a Type and a Value. In this example, it is a Title with the value "PyroManiac". Title, Tag, Color, Cmd and Region type items can be equipped. Title, Tag and Color items go in the slots under the marked areas. Such as:
Click an item to pick it up, click a slot to put it down or click another item to swap their positions. Note that you cannot swap an item if the slot is an equip slot such as Tag, and the item you are swapping is not a tag