The House of El Command Key was a Kryptonian liquid geo Command Key created by Jor-El that he sent to the planet Earth along with his son Kal-El. It can be used to access a variety of access ports in Kryptonian machinery and devices.
Jor-El formed the Command Key out of metallic liquid on Krypton just before placing his son Kal-El in a ship that would be sent to Earth where he would escape Krypton's destruction. He put the Key in the ship with Kal-El and launched him to Earth.
Twenty years later, when Clark grew into adulthood, he heeded his late father's words and went on a journey to find out more about his origins, with the command key still around his neck. Whilst overhearing two soldiers speaking about an alien ship on Ellesmere Island, Clark traveled there and burred through the ice with his Heat Vision, passing the ship's defenses and plugged his Command Key into a fitting socket, finally bringing Clark him face to face with a projection of his biological father - Jor-El. Jor-El informed his son of his alien heritage and purpose on Earth, before moving the ship to a nearby mountain top. Embracing himself as Kal-El, Clark donned a red-and-blue caped Kryptonian skinsuit and began testing the limits of his superpowers, finally learning how to fly.
Shortly thereafter, General Zod showed up on Earth after Kal-El and the Growth Codex, which was sent with the latter. When Kal-El surrended to be handed over to Zod, he gave Lois Lane his Command Key (behind Faora's back). When Lois was thrown in a holding cell aboard Black Zero, she plugged the Key into a socket, which activated Jor-El's projection, which told her how to defeat the invading Kryptonians (a plan she later relayed to Clark) and promptly guided her to the safety of an escape pod, before changing the atmosphere to that of Earth allowing Kal-El to regain his powers and escape.
The plan as to put Kal's ship aboard a C-17 to use as a makeshift bomb against Black Zero, since a collision between 2 Phantom Drives would generate a Phantom energy singularity, that would re-imprison Zod and his forces in the Zone. Lois tried to insert the Command Key into the ship, but it wouldn't accept it. Unable to put it in, Lois was blown out, as Faora-Ul came to stop the plane and undermine the plan. Fortunately Emil Hamilton managed to work out that the pod needed turning, and inserted the key, activating the Phantom Drive, and sending all things near (including the Command Key) into the Phantom Zone.
With the key currently within The Phantom Zone. It is possible to retrieve the key and Kal-El's Spacecraft. If Kal-El enters The Zone and retrieves the key, he will be able to re-establish contact with Jor-El within the damaged Scout Ship.