Whenever i try to open the game, it says "There should be 'GuiltyForce_Data' folder next to the executable" as an error message and i dont know how to fix it.

You didn't wholly extract the game's archive. When you choose the archive with a game (.7z or .zip), click the right mouse button on it and choose "Extract all" or something like this so that it will extract the whole folder and the GuiltyForce_Data folder will be there. You will be able to run the executable file from there.