RSS is off by default in Moodle sites. To turn it on requires (at least) three levels:

• Server level
• Module level
• Individual resource level

At the Server level:

• Admin > Server > RSS. Turn on RSS globally.
  This doesn’t activate anything; it just makes it possible to do so below.

At the Module level:

• For each module type (e.g. Forums) that wants to use RSS:

• Admin > Modules > Activities > Forum. Turn on RSS for that type of module.
  Again, this doesn’t activate anything; it just makes it possible to do so below.

At the individual resource level:

• For each resource that wants to use RSS:

• Go to the resource (e.g., go to a particular forum)
• "Update this forum" button
• In the RSS section, set RSS feed to "Discussions" if you want posts and comments. Set to "Posts" if you want only posts to be in the feed.
• Set # recent parameter to how many items are in the feed. 5 is common; 10 is common. More for a very active resource.