A rar is an archive, you can extract it with 7zip on windows, or with various other software. To play you need GZDoom, the archive includes it for windows but on other platforms you'll have to figure out how to use it yourself.
Thanks so so much it works! :D I can finally enjoy this great game.
Its pretty easy if you understand the basics of files or if you have dealt with emulators and roms before, I'm just 13 and i could do it!
