"Open" is such a broad term. ^^;
If they're inside of a .rar or .zip, you'll want an archive extraction program like WinRAR.
If they're inside of a .7z or other unorthodox archive file, you might want to try 7-Zip instead.
Once the game is no longer archived (if ever it was), you'll want to load either the .iso or the .cue file that you see. And you're going to want to load it in Daemon Tools (or Alcohol 120%, or programs like them). What you need to do is mount it to the fictional drive Daemon Tools has created.
Once the game is mounted, if it was designed to AutoPlay (most discs are), it should automatically do one of two things:
(1) prompt you to install the game, or
(2) open up the disc's root directory inside Windows Explorer (or whatever directory explorer you have)
Otherwise, open the disc's root directory yourself (which would be X:\, where X is the letter of the virtual drive you have created in Daemon Tools or Alcohol 120%)
If it prompts you to install, then great: balance doing as you like with doing as it tells you to ;D and it should work out. If it doesn't prompt you to install, try searching for "INSTALL," "SETUP," or similarly-named files. If you can't find these, consider searching for any executable (.exe) which has all or some of the letters from the title of the PC game in it (e.g. "twnship3.exe" for a hypothetical game called Township 3: the Fall of Gorn).
Sorry if you knew all this already. But like I said, your request is pretty broad, so I have to start from the bottom and work my way up. ^^;
