Once your printer arrives, I recommend you begin by printing off a test label to be sure everything is set up properly. You’ll do this by going to ‘Settings > Shipping and delivery’ from your Shopify admin. Scroll down to the Shipping labels section and choose Print test label. More detailed steps are found in the Help Doc for Printing a Test Label.
When you are happy with the set up, printing shipping labels for your Orders will be done from within the order itself when you go to fulfill it. On the order page, click on the Create shipping label button, as seen below, where you’ll then be able to choose and adjust your shipping option and proceed with printing the label. Take a look at the Help Doc on Shopify Shipping labels for regionally specific steps and information to completing the purchase.
Hope this helps. Let me know if you have any other questions along the way!