GOG is easy as pie. You buy it, you can download it (DRM free) at whim - it’s just an .exe file you can run/install however you prefer. It comes patched, iirc, even, so you don’t do anything else except pull down the Co8 stand alone .exe and run that next (grab the version of Co8 that has extra content - the extra content is seamless, you won’t even know it’s new or what came with the vanilla game, let alone was was restored content lost due to Atari’s interference).
Once you install Co8 you don’t launch the game .exe from the game directory, rather you launch the Co8 front end menu, select a few custom preferences (like how many party members you get to hand craft vs. how many are NPC only, or if characters get max HP at level up, stuff like that), and click PLAY. Then you’ll spend probably the next 30 minutes making characters, and you’re off to the races.