dont understand gearing

[t-maxxracer32]

well ive been trying to learn about gearing but it just doesnt make sence to me!! i know the lower on the pinion and higher on spur is more acc right?...
1. well how can i make my truck get cooler?
2.you can undergear and overgear?
3. how do you know if you undergear?
4. if i got a 60t spur and a 35t pinion what would happen? that is a 1.71 ratio
5. if i got a 96t and a 12t pinion itd be a 8 gear ratio what would happen?
7. what does gear it up and gear it lower mean?
8. if im in the desert with soft sand what should i do with my gearing?
9. also what about the track
10. also what about the street for most speed.

thanks for ansering my questions lol....