search for public keys at http://pgp.mit.edu/
and add it to your public keyring:
 gpg --recv-keys 0xKeyID

import from a file signature:
gpg --import myfriend.asc

trust a particular key:
gpg --list-keys
gpg --edit-key KeyID
trust

WARNING, make sure you revoke first
make a new key and delete the old one:
 gpg --edit-key 0xKeyID
 addkey
 key 1
 delkey
 save

revoke key:
 gpg --edit-key 0xKeyID
 key 1
 revkey?
 save
gpg --keyserver pgpserver.com --send-keys 0xKeyID


encrypt file to various recipients:
gpg -u myuser@mydomain.com -s -e -r user1@domain.com -r user2@domain.net secrets.txt

export/import private key:
gpg --export-secret-key -a mykey@domain.com > myprivatekey
gpg --import myprivatekey

export public key:
gpg --export -a mykey@domain.com > mypublickey

revoke certificate:
gpg --output pgp_revoke_certificate.asc --gen-revoke mykey@domain.com