There are three combo shots, two 3-way combo's awarding 1 million points, and one 2-way combo, awarding 500.000 points. You've got 5 seconds between shots (by default).
Shoot the left ramp, then shoot the back loop, finish with shooting the right orbit.
Wait till the ball drains from the bumpers through the gap, then shoot the back loop, finish with shooting the right orbit.
Shoot the back loop, finish with shooting the right orbit.