To encrypt and sign a plaintext file with the recipient's public key
gpg --encrypt --sign --recipient <recipient> <file>
To sign a plaintext file with your secret key and have the output readable to people without running GPG first
gpg --clearsign <file>
To decrypt an encrypted file, or to check the signature integrity of a signed file
gpg [-o <output file>] <file>
To generate your own unique public/secret key pair:
gpg --full-generate-key
To add a public or secret key file's contents to your public or secret key ring:
gpg --import keyfile
To extract (copy) a key from your public or secret key ring:
gpg --armor --output <keyfile> --export <userid>
or
gpg --armor --output keyfile --export-secret-key
To view the contents of your public key ring:
gpg --list-keys
To view the "fingerprint" of a public key, to help verify it over the telephone with its owner:
gpg --fingerprint userid
To view the contents and check the certifying signatures of your public key ring:
gpg --check-sigs
To edit a key:
gpg --edit-key userid
To remove a key or just a userid from your public key ring:
gpg --delete-key userid
To permanently revoke your own key, issuing a key compromise certificate:
gpg --gen-revoke userid
To disable or re-enable a public key on your own public key ring:
gpg --batch --edit-key userid disable
or
gpg --batch -edit-key userid enable