good tutorial: https://www.devdungeon.com/content/gpg-tutorial

=== To Encrypt/Decrypt a File ===

  gpg --encrypt --recipient 'user@emailaddress.com' example.txt
  gpg --encrypt --recipient $USER example.txt

  gpg --decrypt example.txt.gpg
  gpg --output example.txt --decrypt example.txt.gpg

=== Create a key ===

  gpg --gen-key
  gpg --full-generate-key

=== Show keys ===

To list a summary of all keys
  gpg --list-keys
  gpg --list-secret-keys

To show your public key
  gpg --armor --export

To show the fingerprint for a key
  gpg --fingerprint KEY_ID

=== Search for keys ===

  gpg --search-keys 'user@emailaddress.com'

=== Export/Import keys ===

  gpg --output ~/public_key.txt --armor --export KEY_ID
  gpg --output ~/private_key.txt --armor --export-secret-key KEY_ID

Retrieve the key files which you previously exported.
  gpg --import ~/public_key.txt
  gpg --allow-secret-key-import --import ~/private_key.txt

Then delete the private key file.
  shred -zu ~/private_key.txt

=== Delete key ===
Retrieve key ID then delete
  gpg --list-secret-keys
  gpg --list-keys
  gpg --delete-keys ID
  gpg --delete-secret-keys ID