"If you let the energy in your own body flow, the lightning will follow it. You must create a pathway from your fingertips up your arm to the shoulder, then down into the stomach. The stomach is the source of energy in your body; it is called the sea of chi. From your stomach you direct it up again and out the other arm. The stomach detour is critical; you must not let the lightning pass through your heart, or the damage could be deadly." - Iroh
Lightning redirection is a skill developed by Iroh in order to redirect lightning and electricity fired at him. He developed the technique by studying Waterbenders, who redirect an opponent's energy rather than facing it head on. The technique itself does not generate lightning, and merely redirects it as demonstrated here:
But I wonder if this is a Firebender-only technique, because it deals with lightning, or is it something that everyone can learn because it is a technique dealing with movement and chi rather than traditional bending?