If you have created backorders for your sales orders you will need to be able to track when you have received all of your products.
First, go into the sales order that you have created a backorder for. On the right hand side of the sales order you will be see the field displaying the purchase order you are waiting to receive. If there is more than one purchase order you will see those too.
Select the purchase order listed and receive your products.
Once you have received your products you will be able to see this reflected in the Sales Order.
Alternatively, you can use your filters under sales orders to view the orders that are ready to be shipped.
Go to your Sales Order and click on +Filter. From the dropdown box, select Shippability Status.
Then set the filters for Shippable or Partially Shippable.
You can now view the orders that are ready to ship, or are awaiting to receive.