Will not write yet another tutorial about how to setup GPG. I will link to the ones that I used to do several things.

Settup up GPG

https://oguya.ch/posts/2016-04-01-gpg-subkeys/

https://blog.tinned-software.net/create-gnupg-key-with-sub-keys-to-sign-encrypt-authenticate/

Setting up subkeys

https://oguya.ch/posts/2016-04-01-gpg-subkeys/

https://wiki.debian.org/Subkeys

Setting up GPG for SSH authentication

https://gregrs-uk.github.io/2018-08-06/gpg-key-ssh-mac-debian/

https://ryanlue.com/posts/2017-06-29-gpg-for-ssh-auth

https://opensource.com/article/19/4/gpg-subkeys-ssh

FAQ

https://security.stackexchange.com/questions/206072/how-do-i-interpret-output-that-produces-gpg-listing-keys

https://superuser.com/questions/1371088/what-do-ssb-and-sec-mean-in-gpgs-output