It’s called Radio Relay (narrow beam - line of sight communications) and it’s been around since the 1960’s.
Basically the same as your cell phone. Your signal is picked up by a ground station which transmits the signal to a satellite station in space (the relay) which in turn boosts the signal and returns it back to ground repeater stations over a wider area.
In space though the signal passes between orbiters around Mars and passed down to the Rovers.
Instructions are sent in a compressed computer file which will probably be unpacked on the rover and sent across to the computer on board the helicopter. A bit like downloading a TEF file and executing it in TefView.