What does it mean on the wall plate for a 2, 3, or 4 wire systems: Use RC-RH jumper wire? Is a jumper wire simply a wire connecting RC-RH?

Yes its simply a jumper system. 2 3 or 4 wire is for the unit and its controls.
What type of system do you have? Gas? Ac? Heatpump? Oil? Tell us more info so we can try and help. You might not have the right type of thermostat at all.