Creating a carrier & service for marking orders as externally shipped

Navigate to “Admin” and select “System”
Go to the “Shipping” tab and select “Carriers”
Select “New Carrier Account.” From the dropdown, select the carrier you would like to add, check the boxes that apply and Save. Use "Other" as the carrier to input an carrier name you like. This does not have to be an actual shipping carrier. It can be something, such as "Pickup"
Once the carrier account has been saved, Select “Services”
Choose the Carrier in the dropdown and select “Add Service”. In Service Name, it must match the existing Service Name exactly if you're looking to align with any external system's shipment updates so you can copy and paste, including any symbols. The Service Code must match the value of the Ship Via field exactly as well if you are looking to use the Ship Via field to map carrier & service selections for imported orders. Repeat until all services have been added.
You're done!