Go to Sales Orders and select the orders that you want to create shipments for. Click on Bulk Actions, then select Fulfill Orders.
The following popup will appear:
Check or uncheck that box to decide if you want email notifications to be sent to your order recipients, then click on Proceed.
If you wish to fulfil the order on Shopify, Select "NOTIFY CUSTOMER OF SHIPMENT - Send shipment details to your customer now" on Shopify. The order will sync to QuickBooks Commerce as Fulfilled but QuickBooks Commerce will not send a duplicate email notification of shipment to your recipients.