Ratings
There are likely two issues rolled up in your concern: a) rating not changing, and b) rating changing in a way not understood.
a) The first of these is almost assuredly due to playing an UNRATED game. It is very easy to get one of those if you simply quickly select a challenge or make one of your own without paying close attention to RATED vs UNRATED.
b) chess.com uses the Glicko Rating formula. It is quite complicated. But the short explanation is that your rating adjustment in a RATED game will be based on 1) game outcome, 2) both players' ratings coming into the game, and 3) frequency of play by both players (as exhibited in the RD factor).
Here's a link to get you started on b):
http://support.chess.com/Knowledgebase/Article/View/16/0/how-do-ratings-work
schoolboy, the game you resigned, you lost 6 rating points ... RATED game.
The game you won, you got no rating points because the game was UNRATED.
We simply must look closely to the games we play to notice whether they are RATED or UNRATED ... if we care about rating points, that is.
You make a good point: the rating thing can become a needless obsession and completely distracting to learning and/or having fun. However, when looked at reasonably, it can also be a long term indicator of progress in the learning category. However, on balance, I think too many players get their priorities twisted pursuing ratings. If one learns and improves, eventually the rating will reflect this.