I need a Gear Ratio guide for dummies

[Muzzie]

Can someone point in the direction of a dummies guide to gear ratio's?

I'm running a CAT SX with the internals gears:

23t Layshaft
33t Idler

How do I work out the ratio?

Also the motor I'm running is a Fusion Exceed 6.5t and I've been using different pinions from 22t to 24t with the standard spur gear. The motor user manual does give any recommendations to what gearing to uses, so I'm a bit confused .

How does it work, the less (t) on the pinion the more stress to motor is under / the hotter it gets and the faster you go?

Can anyone help me with a good base line setup for a beginner?