Some light reading for you:
http://www.chess.com/article/view/chess-ratings---how-they-work
Not really.
I don't really care about my rating so I don't really care to dive into it more.
That post is from Erik (of "Erik, the founder of chess.com" fame) so I point people there.
I don't think it works exactly like this, but it's approximately like this...
RD is like a multiplier. If you beat an opponent rated 100 points higher lets say the formula gives you 3 points, but then at the end we use the multiplier. The bigger the multiplier (RD) the more you're going to get. In this imaginary case 3x42 = 126 so you'd get 126 points.
The more often you play, the lower your RD... which makes sense. If you've been playing often your rating is more reliable and doesn't need to change much.
In contrast, new players have a high RD and actually do gain and lose over 100 points for a win or loss. As they continue to play, this change gets less and les of course.
Is 42 a high or low RD comparatively? I don't know. IIRC from when I used to play on FICS an RD of 42 is actually a low RD. So you'd be expecting rating changes of 10 points or under. RDs e.g. 250 were really high and you'd be getting those >100 point changes.
What does that mean.