There are times when you want to tell someone your site’s feed address or URL, or you need it to submit it to search engines and directories, many of which now accept feed URL submissions. There are four possible URLs for each of your feeds. Any of these will work.

http://example.com/wp-rss.php
http://example.com/wp-rss2.php
http://example.com/wp-rdf.php
http://example.com/wp-atom.php

Or you can access them like this:

http://example.com/?feed=rss
http://example.com/?feed=rss2
http://example.com/?feed=rdf
http://example.com/?feed=atom

If you are using custom permalinks, you should be able to reach them through this usage:

http://example.com/feed/
http://example.com/feed/rss/
http://example.com/feed/rss2/
http://example.com/feed/rdf/
http://example.com/feed/atom/

You can also provide feeds to only specific categories on your site by adding the following to the end of the link:

http://example.com/wp-rss2.php?cat=42
or

Adding Feeds

Not all WordPress Themes feature all of the RSS Feed types that are available through WordPress. To add a feed to your site, find the location of where the other feeds are, typically in your sidebar.php or footer.php template files of your Theme. Then add one of the tags listed above to the list, like this example:

 
Adding Graphics to Feed Links

Many people like to have a graphic representing the feed instead of words. There are now standards for these graphics or “buttons”, but you can make your own to match the look and colors on your site.

To add a graphic to your feed link, simply wrap the link around the graphic such as:

<a href=”<?php bloginfo(’rss2_url’); ?>” title=”<?php _e(’Syndicate this site using RSS’); ?>”>
<img src=”http://www.mozilla.org/images/feed-icon-14×14.png” alt=”RSS Feed” title=”RSS Feed” />
</a>

 
Changing Addresses

If you are currently using other webblog software and are changing to WordPress, or are moving your weblog to a new location, you can “forward” RSS readers to your new RSS feeds using file rewrites and redirects in your .htaccess file.

Edit the .htaccess file in your root folder, if no file exists, create one.

Here is an example for a b2 feed:

RewriteRule ^b2rss2.php(.*)? /wordpress/?feed=rss2 [QSA]

Here is an example for MovableType Users:

RewriteRule ^index.xml(.*)? /wordpress/?feed=rss2 [QSA]

Feed Director provides rewrite rules for common feed filenames used by other blogging platforms, such as index.xml, index.rdf, rss.xml, rss2.xml, atom.xml, *.xml, via an easy-to-use “install it and forget it” plugin.

Hopefully this will help all you new to wordpress on one of the most basic questions that is asked. After all, the more people that know about your feed the more exposure your site will get on the web.

sources: http://codex.wordpress.org/WordPress_Feeds