orting a table by the last_name from another table

[PAVB]

If it's an improper questions, just say so

Relax, all questions are proper...

How do I sort the list of publications by the last name of the first author?

What tells you in your data structure which one is the first author?

and I suppose I'd also like to know why I can't use a comma, or how to use a comma, when I'm concatenating two fields

There is nothing wrong with it, try something like...

select a_fname || ',' a_lname
from publications_authors
where rownum < 2;

... just to test it.