Physics

Unity is an amazing program, the possibilities seem endless, and for the most part it is not too difficult to use.  However, collider physics nearly sent me to an early grave.  

The following links helped me grapple with physics.

Unity Docs - Colliders

Unity Docs - Mesh Colliders

The most helpful answer of all time!!!     Guidelines for using Colliders and Rigidbodies

The previous link helped me finish the game.  I spent days and days making zero progress and had tried every manner of google search to no avail.  I accidentally found the above answer and after reading it once, everything seemed to make sense and I understood why the things in my game were not working.  Nothing was colliding correctly, and the bullets kept going through the floor.  There was only so much one can learn from a tutorial, they are only guidelines.  It took another few days but I managed to re-work all the objects and characters and finally they were interacting as they should.