If you're using Shopify Shipping, then follow these steps:

1. From your Shopify admin, go to Orders.

2. Click the number of an unfulfilled order.

3. To buy a shipping label for your order, select Create shipping label.

4. From the Fulfillment page, change the number of products that you want to fulfill for each line item in the Items section.

5. Select the shipping method in the Shipping service section.

6. If you want to send a notification email to the customer right away, then select Send shipment details to your customer now. This option is available only if you have an email address for the customer on file.

7. Click Buy shipping label. The order screen updates to display the order's Fulfilled and Unfulfilled items.