This support article covers how to create a custom shipping provider in Lead Commerce.
Navigate to Sales > Configuration > Shipping Providers and then select the Create Shipping Provider button.
Type in the name of the custom shipping provider. Examples of this could be "Shipping" or "LTL" or the name of the shipping provider like "ABC Trucking".
Add your custom shipping classes by clicking on the Classes section and then selecting New Shipping Class
Fill out the custom shipping classes window and then save and close
Add as many classes as you need for this custom shipping provider. Once you have added the custom shipping provider and classes, remember to map them to either your Customer Types or Sales Channels. See this article for further information.