There are two ways
1)Hill matches - King of Hill, Tsar of Hill, Mayor = Yout challenge current champion of hill, winner gets 10 extra points to rankings, non winner gets 2 points to offset loss in rankings
2)Any non-hill matches reported in the battle reporting thread
The way the rankings go, whoever loses goes down 1/8 of teh difference in rankings. The winner goes up 1/8 ofthe difference if higher ranked, but goes up 1/4 of the difference if lower ranked.
So you boost your rankings by battling higher ranked players (and winning) or by battling on hills a lot.
It is not really a measure of how good you are more how much you contribute to the battling at BABA, but it can be fun (and competitive) if you get towards the top