Since this version of SMF does not really tell you about customizing your RSS-feeds and the default is 5 latest posts no matter where you click on the RSS-icon, I'll type a few helpful RSS-feed examples for you.
This feed will show 10 latest topics from a selected board.
http://www.hard-light.net/forums/index.php?type=rss;action=.xml;board=132.0;sa=news;limit=10
132 is number of News & Announcements board, you can view each board's number by hovering your mouse above a board link. Limit value is how many entries will be displayed.
This feed will show 10 latest posts from a selected board.
http://www.hard-light.net/forums/index.php?type=rss;action=.xml;board=132.0;sa=recent;limit=10
You'll find many more RSS-examples from
here.
Edit: You can also display RSS feeds in your website by using Javascript or PHP script.