Looking for a good GPG guide

For those who don’t know, GPG is a privacy software that allows us to encrypt our emails and much more. But it is not user-friendly at all. Some extentions to mail clients might help (like enigmail for thunderbird)

I want to do GPG “the hard way” - on the command line with offline keys and key rotation, ability to sign other’s keys and all.

Request: does any of you have a very good guide for that?

Most of the ones I find are either incomplete or too simple for what I want.