This page can be reached by visiting Shipping -> Carriers in the admin panel. It displays a list of all carriers that have been added and allow to add, edit or delete them.
The related code can be found in following locations:
Once opened, the page will show following blocks:

The name of this card is ShowcaseCard::CARRIERS_CARD and it can be closed by clicking the x button in the top right corner. The card is displayed only once per employee.
You can check the status of this card by querying the GetShowcaseCardIsClosed query.

Show list of carriers with the ability to filter, sort them and perform actions like activating, deactivating, editing or deleting them.
The related code can be found in following locations: