Questions[keyrings](ubuntu)

Setting up keys for a local repository on a new ubuntu 20.10 virtual machine, I got a message that apt-key add was deprecated and I should read the apt-key(8) man page. The apt-key(8) man page is a collection of words strung together, but if it contains information I can't winkle it out. Can anyone tell me what, exactly, I should type on my terminal instead of:

apt-key add name-of-file

The command does apparently still work after honking at me, so I was able to proceed, but would like to know what I'll need to do in the future.

Some program always asks for my login password. I do not know what causes this. How can I stop it?

I know how to disable it, circumvent it, and that it saves stuff. However, when asked "what is it for, why is it there, and how does it work" I'm at a loss for words. What's more disturbing is there doesn't seem to be much of anything content-wise for those questions on the internet.

So once and for all. What is a Keyring, why is it on my computer, and how does it work?

Can someone please explain what Ubuntu's keychain or keyring is, as well as use cases for it?

Whenever Ubuntu boots up, a dialogue pops up asking me to unlock my default keyring.

Is there some way this can unlock automatically through PAM or some other magical way?