So basically when it launches the game, instead of getting car models from: Grand Theft Auto V/./././vehcles.rpf, it would get them from Grand Theft Auto V/mods/./././vehicles.rpf. This will put that file in the mods folder of GTA V, which will be loaded by OpenIV when you start the game. When you go to edit any RPF or important file, or you go to replace files that were included with the clean game, right click on the item you are going to edit/replace and click 'add to mods folder'. Make sure you install all 3 items by clicking 'install' next to each one Open OpenIV and install the ASI Loader and such under 'tools > ASI Manager'.
There's really no way to fix it now unless you reinstall the game, but in the future, when installing mods to GTA V, follow these steps: