Caveat: IANACarrier sailor.
The catapults have their own steam system, making them independant of any other steam loads on board the carrier. The shuttle (the part that pulls the aircraft down the deck) is attached to a piston, and runs along a precisely-laid track built into the flightdeck. The connection between the shuttle and the piston is sealed by a pair of heavy rubber gaskets that flap closed before and after the connecting arm. Obviously, this isn’t precisely steam-tight (you always see some escaped steam after a cat shot), but it’s close enough.
An aircraft is taxied into place and connected to the shuttle by a bar that projects to the front of the aircraft’s nose gear. In the case of aircraft that don’t have the proper equipment, a ‘bridle’ is used instead (the ramps at the end of the catapult are there to stop the bridles after they release the aircraft and the suttle stops: The bridle whips over and slaps onto the ramp). The aircraft and shuttle are held in place by a restraining bolt of specifically callibrated breaking strain. The exact weight and type of the aircraft are fed into the launching system, allowing the correct amount of launching force to be calculated and set. When all is in readness, the launching trigger is pressed, steam floods the piston, and when enough force is achieved, the restraining bolt breaks, the piston, shuttle, and attached aircraft shoot down the deck. At the end of the run, the piston and shuttle slam to a stop and the aircraft goes flying off into the wild blue yonder.
Flightdeck crew, please correct any over-simplifications and errors…?
Landing is kinda similar, but far harder. The aircraft enters a landing pattern that places the aircraft approaching the stern of the carrier at an angle, on a very precise and narrow flight path. A system of stabilized lights and lenses create visual aiming system (the ‘ball’) to aid the pilot, who is flying one of the toughest routine flight profiles in the world at this point. The pilot’s job is to crash into a moving, pitching, rolling ~100’ by 100’ square at roughly 130 knots. Waiting for the pilot are a series of arresting wires, placed across the deck. These are attached to a variable counterweight system below decks. The arresting systems is also callibrated to the type and weight of each aircraft in turn. When the plane hits the deck, the pilot firewalls the throttles, in case he missed all wires. At the rear of the plane is a hefty hook which grabs (hopefully) an arresting wire. The wire runs out, the energy being absorbed by the counterweights and buffers below deck, slowing the aircraft to zero speed in about 400 feet. The aircraft is unhooked and taxied out of the landing area, the wire is pulled taut back into position, and 30 seconds later, it all starts over again.