Why do you need to setup order statuses?
Every order has its status for payment and for fulfillment. According to the store settings, the Payment Status shows the state of the order’s payment while the Fulfillment Status shows the stage of processing.
This is a very important step you need to take to be able to get insights on what you really need. If you don't set up your order statuses correctly, you will see data that you are not interested in.
Tick the order statuses that you want to see in your reports and that's it. You can change your setting anytime.