I don’t know how to open a .lua file, can someone help? I’ve tried but it doesn’t seem to work.
Notepad is all you need to open it.
Thanks, but I do want to open files in-game, I want to see how the cars perform. I’m running a competition and people send me their cars.
The LUA file has to be in the Documents/Automation/Models (or /Platforms or /Engines) folder for them to appear in-game, otherwise all you get in Notepad is a bunch of encrypted nonsense. 
Drop the .lua file into your c:\my documents\automation\models folder then load the game all files ypu copied should appear in the sandbox list.
The good news: I found out how to do it! 
The bad news: I had to move the automation file, then when I started it, all my cars and engines and stuff was lost -.-
What do you mean by “move the automation file”
Originally, I tried to access the file, but it only sent me to the files which had the bodies, engines types, materials etc. so I moved it to a different area, and then I was able to access the actual saved items.