Basic stuff: Any exposure (Ev) is a combination of aperture (Av), shutter speed (Tv) and ISO (Sv in Pentax-land). So the light meter says "this looks like Ev 10" and you're in Program mode. The camera has to choose among many possible Av/Tv/Sv combinations that work out to Ev 10. The Program Line setting allows you to influence its choice.
Normal is going to pick a setting in the middle of the chart of possible values. It won't be biased to maximize shutter speed or choose the sharpest aperture.
Auto chooses from one of the other 5 program biases. I read somewhere that Auto is influenced by lens choice, subject distance, maybe SR too. For example, with everything else identical, you mount the kit zoom set to 35mm, then the DA 35mm f2.8 Macro. Auto will think that the kit lens only deserves the Normal program, but you chose the macro for a reason, so it might bump ISO to allow higher shutter speed, desirable for a flower on a windy day.
Depending on the lens and conditions, you may not see any difference. In low light, there may only be one practical combination - Av wide open, Tv at 1/focal length, Sv as high as possible. The program can only do so much. Even with options, the choices will be subtle, not dramatic.
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