Your Stock level report is where you can track your inventory level: On-Hand, Available, Reserved and Incoming.
You can find this report by going to the Menu 'Inventory' > 'Stock level':
Of course, you can filter your Stock level by product, location, supplier,... For more information about using filters, please refer to Filters and Views
For each product, you will see the following information:
- The On-Hand inventory is the quantity physically present in your stock location (warehouse, truck, office, basement,...).
- The Available inventory is your On-Hand inventory minus the products currently in Sales Orders but not yet included in Shipping Orders. The latter is called Reserved inventory.
- The Incoming inventory is the quantity of products included in Purchase Orders but hasn't been received yet.
You can also display the same information, including Bin Locations for each of your stock locations by clicking on the down arrow sign:
Erplain allows you to see snapshots of Sales order and Purchase order in your Stock level menu. If you click on the "Reserved" or "Incoming" quantity of a product, you will be able to see all the sales order or purchase order this quantity is coming from. 
Here is how your inventory is updated based your Sales workflow:
For more information about the Sales workflow and the inventory update, please refer to this article.