Using Auto - a camera sets for me the aperture and shutter speed .
If I want to do it myself, how to set right parameters? Does it only
practice or exist the rules that will help me to set the "correct" or close
to correct params?

if my subject 5 ft and 500 ft away from me and at both cases at the center
of the frame how the params will change , and if I need at both case keep
only subject at focus, does it possible?

Can reference me to any sourse where I can find answer on these and related
questions (not only that smaller aperture increase DOF)?

Thanks