[Shabbadoo]

I've been playing guitar for almost 2 years now, but only on accoustics, and I just bought a new electric guitar. This guitar has screws that can be turned to adjust the position of the bridge for each string.
If anybody can explain this to me, how does adjusting this effect the sound/tuning of the guitar? Is it even something that I should mess around with at all?

One thing I have noticed is that sometimes, the D string has a slight rattle when it's being played. Could this from the string rattling on another fret further down the fretboard from the one I'm playing? If so, will adjust the bridge bring the string a bit further off the fretboard to help prevent this rattling?

Thanks.