There is a lot of information around for the emacs OS. Most people probably know about the emacswiki, which probably the single most useful resource in connection with the emacs manual and the emacs lisp reference manual.
Those resources are static, though. Sure, the manuals are updated as emacs changes and people update and improve the wiki as well. But by and large they are fixed resources.
But there are also a lot of resources on the web, that feature emacs-related stories on a regular basis as well. Some are collected via Planet Emacsen, but even though I don't want to sound too harsh, I think that the signal-to-noise ratio is a bit low over there. Here are a few sources of periodically updated emacs resources, that I actually enjoy:
Blogs:
Emacs-Fu: Dirk-Jan Binnema's blog (otherwise known as "djcb"); around since 2008; this blog was one of the most helpful resources, when I made the transition to emacs.
Mastering Emacs: Mickey Petersen's blog; younger than emacs-fu: started in 2010; original idea was to close the gap between the emacs tutorial and the knowledge required to understand how the emacs cosmos works; very neatly organised.
Emacs Redux: Bozhidar Batsov's blog; started off in March of 2013, so this is the youngest of the mentioned blogs; always picks one topic and discusses in just about the right amount of extend; never too much, never too little; you should take a look.
Screencasts:
Emacs Movies: This series by Noufal Ibrahim features in depth looks at different features and add-ons to emacs; lost a bit of steam in the last few month, but screencasts of that magnitude surely take a large amount of time to prepare.
Emacs Rocks!: These are Magnar Sveen's short takes on interesting emacs features; short, sweet and entertaining; Magnar also has a blog: What the .emacs.d!? which I find a bit too terse, though.