After downloading the .lua file. Cut (or copy) the file into your C://Games/Toribash/data/scripts directory.
Then to open it just go into Setup > Utils > Scripts in toribash.
That should be it
No, you copy the icon [file] and paste it into your scripts folder.
Make sure it's a LUA file though. If it's not, just rename the file and add a '.lua' at the end.