RSS Feeds for Forums
For forums which have an RSS Feed configured for them, you can enter the forum and select the feed link from the "Forum Options" dropdown.

My Feeds
If the administration has enabled the "My Feeds" option, you can manage RSS feeds from the "Feeds" link in the "My Stuff" dropdown in the navigation area.

From the My Feeds area you can see all of the RSS Feeds available to you, including all of the forums which have individual feeds. You will also be able to retrieve the feeds for your inbox and the global feeds for recent topics. Please note that these may or may not be available based on admin preferences.

Cheers,
Dan