Background= the 'walls/floor/ceiling' of the 3D space....the 'background' of everything---are you in a darkened room or outdoors?
Point Light=??hard to describe...how 'intense' the environmental light is...??
Ambient Color= ...I'd consider this to be, 'houselights', the generic lighting in the environment without any control of fixtures--art it up with some color value, sure go ahead
HTH
Rexy
...easiest way is to just experiment with the slider and see how each affects the environment...