Some interesting resources are out there on the web for those starting out with GNU Screen.
Clear back in 2007, Red Hat Magazine had a nice tutorial on using screen. It provides a brief overview of the basic features and setting up of screen.
Going even further back, in 2004, Debian Administration had an article, Using GNU Screen, that was nice. GNU Screen is also covered in other articles on Debian Administration, including this one (in 2007) on using screen’s multiuser support to allow multiple people to see the same screen over the network.
Another article from Linux.com also described the multiuser feature, and rather well.