[ubuntu] iptables rule selection + new,related coections

Hi all

I have two questions i hope someone can help me with

#1 Does iptables use the first rule that fulfills a criteria, or does iptables read all the rules and select the most specific?

#2 If you have a 3G / 4G router that you wont allow to be contacted from the outside world >but< coections / sessions established from the local network through the router
are allowed to cross in both directions?

I know you can use the new, established and related keywords for this, but i have never quite figured out how and the information ( that i can find ) aren't defining these keywords that well.

Thanks in advance
Kind regards.