The program mode is an automatic mode, like in point and shoot cameras, but allows some settings to be changed.
We set the dial at P.
The camera calculates the shutter speed and aperture as well according to set ISO value and given light conditions.
What setting we can change?
Aperture shutter speed pairs, by turning the dial.
What is it good for?
Point and shoot type lazy photography. Sometimes we get tired after long hours of photography, and just don’t want to mess around the settings. The camera usually wants to use middle apertures. Best fit to general landscapes or street photography, if we don’t care about depth of field.
What is it not good for?
For wildlife with longer lenses not really good, because in this case higher shutter speeds are preferred. Other specialist photography when you want to control the depth of field like macro or portraits it is not the best.
If you really want to learn do the assignment. Make pictures with different apertures from the biggest(smaller number) to the smallest apertures. Study the pictures you make.