a) komi is just the additional points that are added to white's score at the end of the game (not removed from black, although the difference would be the same). It is extra compensation given for letting black go first, though traditionally it is not used in handicap games, or a komi of 0.5 is used to prevent a draw (also the reason it is 6.5 instead of 6). 

b) I've very rarely seen a game where komi was used on a 9x9, but it is a valid question. I've seen a few examples of pro-games on 9x9 and they generally just use 0.5, but that's just what I've seen, most likely not the case in every professionals' games on 9x9's.