DIgital Amateur Radio FCS network explained

I'm new to all of this, and after searching, I'm having difficulty understanding the FCS network and how it al works.

I've been on the x reflector website, but it doesn't seem very intuitive or have much of a description, that I found, anyway.

Are there any resources that explain the system better? YouTube videos? Even basic info like, are the reflectors tied into local repeaters. Like IRLP or Echolink? Or are they just "chat rooms" for digital modes?