PGP provides specification for crypto operations. It is mentioned at RFC4880
Tools
GnuPG is open source tool for PGP related work. PGP provides the specification for PGP.
It
Provides interface to generate keys
Encrypt data
Sign data
https://gnupg.org/documentation/howtos.html
https://help.github.com/en/github/authenticating-to-github/generating-a-new-gpg-key