Duties of a shepherd in a CS conference
in my experience, the shepherd is supposed to produce constructive feedback, and basically setting a shepherd on a paper tells the authors they need to keep working on the paper for as long as possible. Don't worry about it too much, you're not meant to rewrite their paper. Ask the person that set you up to be shepherd whether the authors will know you or not.
You might get mentionned, same as reviewers in the proceeedings, but think of it more as building experience and goodwill in your research network.