Something about every device in your local network being visible from everywhere?
Some claim it obsoletes NAT?
I get that it's probably too complicated a subject for an ELI5, so if there are good videos or resources explaining it in less than half an hour, feel free to share.
It's just a larger address space, nothing particularly special. Just more numbers
If you use IPv6, you don't need to have concepts like rfc1918 / "private ip spaces, so if every ip is unique, they can be used publicly you don't need NAT
MAC addresses are link-local device identifiers, used by the switches and routers and WiFi access points that talk directly to the devices in question. Switches and routers maintain a table of which MAC to send a packet to based on the IP address - I.e. which actual port to send the data frames down.
There is DHCP for IPv6, but the IPv6 stack is supposed to be able to detect which subnet it’s router is in and then just pick addresses on its own (it does look for conflicts before committing to an address). This is called SLACC (stateless address auto configuration).
NAT is unnecessary because there are so many addresses, as others have mentioned; but I did want to point out that NAT is not used for security. Just because it obscures your devices does not make them any safer. All IPS routers have a firewall to one degree or another (could be as simple as “no incoming connections”; which is bad and lazy but it happens). Firewalling - examining incoming traffic against a set of rules for allowing or denying - is the correct way to secure any network, IPv4 or IPv6.