What is the status Of Item/Product Availability Form?

Dear All Experts,

I have checked one Items Availability and gets confused that what information it is showing: Please help to understand there functions, here we are only using purchasing & Inventory Module.

Here you will see so many options, Like starting Qty Available?

Qty Requested?

First Available Ship Date?

now if you see in Demand & Supply Tab:

Demand, Supply & Pegged Qty?

And in Available Quantity Tab:

Available Qty?

Here I am confused that in Available Qty Tab: there is lot of Qty Available , so it can be used ?