It will probably help you most to think of Trigger Ball as a variation of snooker. A variation of snooker with fluctuating gravity points. And no cue. Yes, that will probably help you understand Trigger Ball the most.
What? It doesn't? Well in that case, look at it this way – in Trigger Ball you have to hit all the big balls with your little ball. To do it you'll need to figure out how best to bump angles and work trajectories. Then Trigger Ball introduces other balls that mess about with gravity and, well, that's when things start to get really wild.