question for ya'll

[97CivicBoy]

yeh i got an automatic civic... for regular drive i keep it in d4...what do d3 and d2 do..i use d2 wen i'm goin down a hill to save brakes..but then somen ewas tellin me the other day to use d2 up a hill....i'm confused...ne who..i also hear ppl shift when they wanan race from d2 to d3 to d4...for me however thas so much slower than jus keep it in d4...