When in a quote or an order, you can see what is in inventory stock by clicking on "Tools" > "Stock Status". This will go through the bill of materials for your transaction and find the parts in inventory. You can see the quantities on hand on the right-hand side, under the Consignment or Resell warehouse columns.
When entering items in an Order, you will see local inventory status beneath each item (listed in red). This can also display information such as when an item is on backorder.
You can also get a quick view of all items in inventory by going to the "Inventory" section and clicking on "Show Inventory Stock" in the blue find bar on the right. This will show quantities of items on hand, as well as what is backordered or reserved.