Installing them isn't all that hard, I usually include that kind of information in the script itself
# How to Install:
# • Copy this entire Script.
# • In your game, select Tools >> Script Editor.
# • Along the left, scroll all the way to the bottom
# • Right click on 'Main', and select 'Insert'
# • Paste the code in the blank window on the right
5 Steps isn't too bad, but sometimes you need to do a bit extra, so for some menu systems you'll need to get the icons, and some script aren't compatible (for example, two scripts that heavily remake the battle system probably won't work together).
Just something you need to look out for
As for using them, after you have them installed, there's usually a wall of green text at the start of the code.
Green means comments, they're sections that the programmer has left to let you know what's happening, and they'll usually start the script with the customisation section, where you can tweak the scripts
As for learning, that's what amerk talked about.