RSS feeds advertise them
There is a fair amount of information on how best to get a rss feed set up. This includes placing code similar to the following
[link rel="alternate" type="application/rss+xml" title="RSS" xhref="http://www.yourdomain.com/rss.xml" mce_href="http://www.yourdomain.com/rss.xml" ]
The [ ] brackets should be replaced by < > less then and greater then signs.
The code tells spiders and other automatic search engine driven sites that a feed is available and it can be found at that address. The code should be placed in the header of the html code.
To display a feed in a website here is a tutorial
http://www.small-business-software.net/display-rss.htm
Once the feed is working it is time to promote the site. Feedburn is a great resources to start with. Once this is working submit the rss feed to aggregate sites. This is done very much the same way that that a normal url is submitted to a directory.
Some resources where feed aggregate sites can be found are
http://www.rss-specifications.com/rss-submission.htm
http://dummysoftware.com/rsssubmit.html
