How can I program the master unit and remote unit? How long do I need to depress the "learn" bar?

The RC420 has a unit that plugs into a power outlet and a Xmas tree can then be plugged into the unit. A remote devise, included with the RC420, can then be used to turn the appliance off or on. The main unit has a "learn" button that must be coordinated with the remote unit in order that the remote can be used to turn the appliance on and off. What steps are necessary to marry the two units?

Not sure about Xmas trees, but garage doors are similar. Press the learn button, it should then blink. Hold down the remote button until the blinking stops. Try the remote. Work?