Get Orders lets you set which Shopify Orders Big Business finds for processing.
Open tells Big Business to find all orders on Shopify's open orders list. This includes all new orders, paid and unpaid, fulfilled and unfilfilled. Orders that are Archived are not included, so you can use Shopify's Archive and Unarchive controls as needed.
Set Orders then sets Shopify Orders to Archived so they are not processed again. Orders can still be updated for payment and fulfillment within Shopify.