I've had to teach myself to spin while riding. I have always been a "masher". I'm a big strong gal with big strong legs. It was just easier for me to muscle up a hill than to make the gearing easier and "spin" up the hill. I've since learned spinning is much more efficient.

If you understand the difference between aerobic and anaerobic than you understand the difference between mashing and spinning. If spinning, you are generally in an aerobic mode. If mashing, generally anaerobic. Of course, cycling is suppose to be an aerobic sport so mashing is not that good, although I still like to mash up short, steep hills.

I was taught to find a comfortable cadence, generally 80 - 90 rpms (you use your computer to find this) and then set the bike in a easy confortable gear where you can maintain this cadence. If you are "bouncing" on and off the saddle the gear is too easy. If you are pushing down on the pedal the gear to hard. You should be rotating or "spinning" your feet in a smooth, round pedal stoke to maintain the cadence. Takes practice but once mastered, your cycling will really improve especially hill climbing. The key is to keep your cadence around 80 if possible up a hill. Only way to do that is to lower the gearing and spin.