What do you guys, and girls do when you come a cross a RGSS script, or MV Plug in you want to use but don't understand how the system works? I ran into this problem many times. XD
Look at the comments at the beginning of the script. They usually have some form of instructions as to how to go about using the script, or if it has any dependencies on other scripts.
Though, to be honest, I'm kinda terrible at annotating scripts, since I'm not even sure if my home-brewed crap scripts will work at all the way I think they will!
The author usually either puts in a short paragraph of what the script is/does at the beginning, or makes descriptive annotations next to settings you modify.
Basic knowledge of coding and modules definitely helps, too. So even if the author doesn't provide documentation, playing around with settings should help you understand them.