This is your complete inventory. If you select "Do not sort" you have the full contents of your inventory here.
When you go in on an item in your inventory, you can see the value of your item, sell it back to the game, post it in auction or send it via mail.
You can also Disenchant most gear if you have the profession Enchanting. Then you can get reagents for making enchants! Higher tier gear give higher tier reagents for enchants.