Without more information we can’t really help you out that well.
That game you’re looking at is GTA 2. It was free for a while and you could download it from Rockstar Games, but apparently it is no longer. Inside FiveM you can actually run around on the map using your arrow keys. I haven’t found a way to enter a vehicle, but I must say I haven’t really tried that hard either.
If you’re experiencing issues, clicking “localhost” will not start a server automatically, you’ll have to host FXServer yourself. You can get started by looking at this or this.