Curving simply means that the final score (range of 200-800) on each section is equivalent to the same score on a different testing. There is not a straight line correlation between your raw score (+1;-1/4 scoring) and the scaled score. On a particularly difficult test, you might be able to get 2 wrong and still get an 800, while on another test you might have to have a perfect raw score to get an 800, 2 skipped might get you 790, and 2 wrong might get you 780.
If you use score choice, you can send whichever scores you want, and not send others - however, you cannot choose individual section scores to send. You send them as a full sitting. So if your first try you do well on the Math but lousy on the CR or Writing, and the second time your Math score goes down, but your CR and Writing go up, it is still in your best interest to send both. You can't superscore yourself, and most colleges will use your best scores anyway.