Processing to arduino with key press help

[jiokl]

I'm trying to control a stepper motor and turn on and off a relay with key press. What I would like in the end is by hitting one key (for example "A") it would make the stepper go to the left, and when I would hit another key (for example "D") it would make the stepper go to the right, and when I press a key (for example "S") it would turn the relay on and keep it on for as long as I held down that key and when I release it turn off the relay. I haven't used processing to arduino before so any help on this would be amazing and I would be very grateful.