CIDR and NAT doubts

I'm studying networks.Can you please clarify soime doubts for me?

1. Is CIDR used nowdays or we only use NAT? If yes, in what occasions?
2. How does the CIDR routing works? I mean, how does the router knows what is the terminal it has to make the data arrive?
3. same question as 2 but for NAT.
4. I understood this, but is it true?-> using CIDR, 100.30.1.10/16 is different than 100.30.1.10/24, so they identify 2 different networks, the first with 2^16 possible hosts and the second with 2^8 hosts.Or maybe it's that they are somehow the same big network and the second identify a subnetwork inside the supernetwork?
5. How does IPv6 will handle subnets?