Pending orders are orders for which the payment from your customers has not yet been captured in Shopify.
You can not process or edit Pending orders on DSers until the payment has been captured.
It may sometimes happen that after you captured the payment of an order, the status of the order remain as Pending on DSers. It is very easy to fix that.
Go to Settings - Other - Sync Shopify orders.
Select your store in the drop-down menu.
Select a date range and click on Sync icon below.
DSers will then synchronize all the orders from the store you selected that you received within this date range.
The orders in Pending for which you captured payment will be move to the Awaiting Order tab.