Short version. Every machine have a score objective (like score based pingolf). Progress towards that objective is how many pins you have hit down. So get it on ball 1, you get a strike. Ball 2 a spare. Duckpin bowling is 3 balls. Scores like bowling so strike adds score of next 2 balls to the frame, spare add score of next ball to the frame.
Pinbowling! talks about the format. I have been wanting to run one of these because it sounds fun and different.