If you want to make a single order are dispatched you need to first open the pending orders screen, (Orders > Pending Sales > All Pending Sales). On this Screen you will given a list of your current orders which need processed. Click on an order to open up more details about the order below the orders table.
On the right hand side of the new area you'll notice an "Item Status" dropdown box. This dropdown will allow you to process the order (Set to "Dispatched"), refund it (Set to "Refunded"), or move it to the picking list (set to "Pick List").
This also allows you to process or refund single products within an order which might have had multiple products ordered. For more information on processing orders in bulk click here