The process to get free games (for pc) is a lot like getting movies with a couple exceptions. Some of the exceptions is what you have to do to use the game. Another thing is the best pace for games is torrents. Lime wire isn't that good for large files and if you found a full "game" on it there is about a 90% chance it will NOT have what you want and not a virus. So once you get your game files (that usually takes a day or two) it will probably be in one or two formats.
Lets talk about the first one. The first type of file type it called an ISO file. Think of this as a digital copy of the disk. To read it you need a (free) program called Daemon Tools. Once you have it, all you need to do is mount it (right click the icon in the systems tray) and load it. Make sure that auto run is enabled then it will run like a real cd. Depending on the game you downloaded it should have the serial keys with it and if you need to you can download a hacked version of the exe (this is the program of the game the thing that launches when you click the icon) There are many places that you can get them on the Internet for example just type in Far Cry 2 exe or Far Cry no cd fix. Then you replace it with the real exe and there you have it a free game (I do not recommend doing this because it is against the law and you could go to jail for a long time).