If you're not familiar with what RSS is about, see http://www.webreference.com/authoring/languages/xml/rss/intro/ for a quick intro (you don't need to bother reading about the syntax, as WSN handles that for you).
When the RSS feeds switch is enabled at Admin -> Settings -> Switches, WSN will autoinclude <link rel="alternate" type="application/rss+xml" title="{SITETITLE}" href="{RSSURL}" > in the head section of your pages to inform web browsers that the page has a feed available. If you would also like to add a link on your page, you can use <a href="{RSSURL}">RSS Feed</a> to the wrapper template at Admin -> Themes -> Manage Templates -> Wrapper. Note that {RSSURL} will usually we a full-site feed, but when you're viewing a particular category it'll change to a feed filtered for the particular category instead.
You can also construct your own feed urls. WSN makes RSS feeds available through the file rssfeed.php. The feed contains a url, title and description. These feeds work basically like toplists. Just as for toplists, you can specify the ordering and type and number of items listed by tacking the info onto the end of the URL. For example:
rssfeed.php?type=links&number=5&field=time&ascdesc=descending
This URL would give a feed of 5 listings, ordered by newest first. If you wanted a feed of 10 comments, you could use
rssfeed.php?type=comments&number=10&field=time&ascdesc=descending
To do only regular listings, you'd use
rssfeed.php?type=links&number=5&field=time&ascdesc=descending&thecondition=type='regular'
To do a feed for a specific category, you would use rssfeed.php?thecondition=catid=10 for category #10. If on the 'show listings in category' template simply use the {CATID} template variable to make it show for every category (catid={CATID}).
Note that only words should be quoted in the condition part of a url, never numbers.
Note that you can do a random order with field=rand()
Note that the RSS stylesheet is at rss.css.
Applicable to WSN Links only: if you wish to have the feed link to the link details page instead of to the destination url, pass &usedetails=1 in the URL.
If you want static versions of these feeds for lower server load, you can use the 'static file generation' area of your admin panel to have a static version of the specific URL you desire saved.
Note that if you're looking to use a complex filtering condition you need to use URL-legal characters, meaning spaces become %20, such as
rssfeed.php?thecondition=catid=6%20OR%20parentids%20LIKE%20'%|6|%'
Types of feeds you can specify in the url:
type=links - listings
type=categories - categories
type=comments - comments
type=cal - calendar events
You can edit the RSS feed content using the RSS feed template, and can use a custom template over it as with any other template by affixing &custom=yes&TID=templatename to the URL.
Location-Based Feeds
If your directory has addresses of physical locations, you can create a feed of listings near a specified location. This example will show the newest listings within 20 miles of the viewer (as calculated by IP address if you have the geolocation database installed):
rssfeed.php?zipmiles=20&zippostal=visitorlocation
This alternate example shows listings within 15 miles of the zipcode 95682 (Shingle Springs, California, USA):
rssfeed.php?zipmiles=15&zippostal=95682
Adjust the URLs as desired.
Speed
In order to save server load and increase speed, you may want to make static copies of key feeds. You can use Admin -> Miscellaneous -> Static File Generation for that.