Typically my knowledge of domains, DNS settings and A-records is happily restricted to one phrase: “Sergio, can you setup a new site please?”
But recently my personal website had issues with the DNS service I was using. I needed to move it, including changing my entire hosting and email. It’s headache material, but it’s one of those things that website owners have to do sooner or later.
If you are also daunted by all of this jargon, this may help:
The small print: this is a highly simplified diagram of how all of this works, intended to only provide an introduction. There are many more connections in between the ones illustrated. This also only shows POP3 email accounts (the most common business setup), but there are other options such as webmail and IMAP.