What roles do the publisher, distributor, and subscriber play in a transactional replication setup?

The publisher is the source database where the original data changes happen, the distributor is a special role, sometimes a separate server, that manages and forwards the captured changes, and the subscriber is the destination database that receives and applies those changes, together forming the complete replication pipeline from source to destination.

-- Configure the distributor first
EXEC sp_adddistributor @distributor = 'DistributorServer';

-- Then configure the publisher
EXEC sp_adddistpublisher @publisher = 'PublisherServer', @distributor = 'DistributorServer';