Is there a A/MX records tutorial?

So an a record is nothing more than a name you connect with an ip address. Your computer takes that name and asks your dns server (in your case hour pi-hole) who that is. Your dns then looks it up and tells your pc that this address is the ip 157.22.4.67 (just made that up and don’t know what’s there). So then your pc connects to that ip.
PCs can’t really work with names and need ip address to reach anything over the internet.
It’s like your home address so that the post office can deliver to you. That means every device that is reachable over the internet needs a unique ip address. Like how your home address that needs to be unique too.

But now comes the more complex part. There is a device that sits between your local network and the internet. Like the door on you house.

Because ip addresses are limited they declared that there should be private ip ranges that won’t be able to be used on the wider internet, and these are 192.168.x.x, 10.x.x.x and I forgot the third range.
These ip ranges are only usable on your network.
They are like little postal addresses that only the people living in your house know and can go there. The postman delivers to your house address and you take that letter and give it to the recipient that maybe lives in a room in your cellar. Your postman doesn’t know but you do. In that case you are the router your provider gave you. That router uses something called a NAT (network address translation) to deliver the package to the device that asked for it. Because most connections are going out from your network to the internet it’s mostly plug and play.

So what you can do is go to your domain provider and change the A record to the external ip address that your router is using but be warned there a countries where the provider changes your ip address with every reconnect (mine does).

And here is the tricky part. Your router needs to know to whom he has to deliver and you can tell him that with port forwarding. That means that if you try to connect with a browser to your external ip address it goes to port 80 if you use http:// or 443 if you are using https:// and your router needs to know to whom these connections go and that should be your server.

And now comes the harder part. You have to have a web server on your home server that uses port 80 or 443 to accept these packages and shows you your sites that you want to reach. I don’t remember much from configuring nginx/apache to help you there but the rest should be searchable.

TL;DR: A records are like postal addresses that say behind that name is that ip address so that a computer can go there.