Find an archive that displays what you want, and add /feed/ to the end
e.g. /category/test becomes /category/test/feed, / becomes /feed/, /books/ becomes /books/feed
If you add /feed to the end of a single posts URL you will get a comment feed
You can also do /feed/rss2 or /feed/atom
RSS feeds should contain a title and content, if an excerpt is shown rather than the full content, you should go to your reading settings and change the relevant option