RSS and Excerpt

Two questions:
1) My RSS link doesn’t seem to work. I didn’t see any installation instructions regarding it either, so how do I get the http://yoursite.com/feed/rss2/ kicking? Is it as easy as creating those catalogues and giving them write permission?
2) Haven’t seen anything about Excerpt either; my question is: if I don’t write anything in Excerpt (when creating an post) will WP revert to the beginning of the post, or will the RSS be empty?