Mods are usually installed by simply over-writing the default game files on your hard-drive with ones given to you by the mod developer, but there are also sometimes more complex installation packages created by the developers. Also, another extremely important word of warning: you should not attempt to use mods with GTA Online! This will very likely result in a ban and is not something that we endorse. Yes, there are mods for the console versions of GTA IV for example, but we aren't going to cover them on this site. Mods really only exist on the PC versions of GTA games because modding on a console is extremely hard and requires a hacked console - not something that we really condone.
