Each provider contains a list of their services you can use. You can enable/disable each service depending on your shop's requirements, as well as renaming them to your needs. By default, all shipping methods are disabled, so you can enable just the ones you want.
Postie supports to manage individual conditions for every shipping category you set up in Commerce. The appearance is similar as the management of shipping rules in Commerce to keep things the same way.
You can find more details about the individual shipping methods for each provider under the Shipping Providers → section.