Get a copy of "Bicycle Gearing" by Dick Marr. It more technical but it will make sense after a second reading.

The Left hand gears are incredibly important. I use the left hand (front Derailuer) each time I ride and will no longer purchase a bicycle without the tripple. The reason being, dropping to the tripple allows me to reach a low gear very fast without having to drop two or three gears on my right hand (Rear Derailuer). Once I get to the top of the hill, I simply click the left hand back to the middle chain ring and I'm finished.