The upper part refers to equiped items, the lower part refers to storage.
The inventory has 90 fields to be store items, 45 on each side. In the lower part of the inventory, it's noted the ammount of yang on the character.
There is also access to Item-Shop Storage, Belt System Inventory, Dragon Stone Alchemy Inventory and Costume System
The inventory is also accessible by pressing the letter "i" while ingame.
Here is an inventory and the function for all the slots and buttons
9- Special items (EXP rings, mounts etc)
10- Access to Item-Shop Storage
12- Access to Dragon Soul Alchemy Storage
13- Costume System
15- Storage for items
16- Belt System Inventory