GeekTool (someone else's great program) is a Mac system preference pane application that puts things on your desktop background, where things are images, files, and scripts (my favorite).
This is my script collection, some written myself and some scrounged from the internet, modified to work (some of them didn't) better (some needed tweaks to be truly useful as GeekTool scripts). You do not need to use GeekTool to use the scripts - they're just useful shell / terminal scripts that display information. While I didn't include any scripts that would harm your system, prudent computer users always read scripts from the Internet before they run them (you, not me and mine, are responsible for your actions).
The main.bash script is just one script that runs all the other scripts. You comment out the scripts you don't want to run. This not only lets you display a set of scripts in one Geeklet, but lets you change your GeekTool desktop display without having to change the script within the GeekTool preference pane.
You can make as many copies of main.bash as you want (rename and change the nameofscript variable) so you can do multiple Geeklets that each run multiple scripts.
Mostly, though... it's just a list of the exact syntax to make the individual scripts work.