How to See Inventory and Use Items
To see your character's inventory, press the "Items" button in the bottom-right of your screen.
If you want to see what an item does, right-click on the item and a screen will pop up, telling you exactly what the item can do. If the item is "useable," double-clicking on it will use it. If the item is "wearable," (like a weapon or a piece of armor), left-clicking on it will equip the item.