This is a good starting point.
The Simpit. Be aware of sponsored reviews.
In my opinion the difference is this.
Video game: Focus is on fun and a feeling of speed. Realism is sacrificed for ease of use and fun.
Simulator: The focus is on realism. The feeling of speed and ease of access is sacrificed for realism. These computer programs go to great lengths to simulate tracks, tyre wear, tyre temps, corner weighting etc as closely to the real world as possible. This often means it is difficult at first to succeed. They also go to great lengths to ensure that the hardware used to control the program convey the feel of the car's movements as closely as possible.
For example. My simulator cockpit has a steering wheel with strong motors that move the wheel and let's me "feel" what the steering does and the grip of the tyres on the surface. The resolution and accuracy of this feedback from the simulator has become much better in the last few years.
Tip: If I were to do this again I would ensure I had a separate room form my simulator where it was always accessible. The hassle of having to rig it up in my living room every time is too much, and I find that I don't use it as much as a really should and would like.