Bicycle Mechanics - Gears?

You've all probably heard me stating the n00b-ness of myself, so here's another death defying question. :(


On the crank, I have 3 sections, on the casette in the rear, I have 7.

What ARE those gears for?

Because, I have never ventured past 3-1 to 3-7

No worries, we all start somewhere.

http://sheldonbrown.com/gears.html

The front 3 give you 3 different ranges:
small ring =low (easy to pedal uphill)
medium
large ring=high (for downhill or tailwind).

In theory you can use any front chainring with any rear cog to give a choice of 21 gears.
In practice, the 3 ranges have a considerable overlap. You can work out the overlap by calculating the ratio in gear inches (http://www.sheldonbrown.com/gloss_g.html#gearinch)

A further practical limitation is that you should avoid the crossover gears which can lead to excessive wear and strain on your chain. Small/small and large/large combos can all be replicated using a straighter chainline.

So, basically...Let's see if I have this right (First number is the crank shifter and the 2nd is the Rear Casette Shifter, The Derailler(sp) )

I'm in 3/3 and down**** to 3/2 then 3/1 and then can I shift to 1/1 without the chain jumping? 1/1 being the small ring.

You need to work out your shifting pattern for yourself, it depends on your exact setup and where the overlap is. I often use different "routes" depending whether I am shifting up or shifting down.

It is best to stick in the middle ring for most riding.
When you get to M/1 (middle ring/largest cog) you can shift to S/1 but this is a big step change in gear ratios. I often upshift to S/2 for an intermediate gear.
On the upshift, I go from S/3 to M/1 to avoid big steps.