A question about bolts.

[Land Locked]

We have a huge pool of knowledge on this forum which I would like to tap.

I've read numerous posts that the bolts we should use should be at least 8.8.

What exactly does 8.8 mean?
Whats the difference between 8.8 and 10.2?
How is this difference achieved?
Is any hardening simply case hardening or right through?
Lastly is there a table available with the information on the different applications?

Regards
Johan