If you know a site or online service with an RSS or Atom feed, you can follow it from the Fediverse using the RSS Parrot service. Instructions for using RSS Parrot are on its website:
TL:DR: Mention the RSS feed's address in a post along with the RSS parrot account @birb
The RSS Parrot account will reply with a Fediverse account you can follow for that feed.
RSS Parrot
Home of RSS Parrot, a free Fediverse service that lets you turn Mastodon into an RSS or Atom feed reader.rss-parrot.net
