Do you have a C terminal in the furnace? If so, then simply connect the orange wire to the C terminal in the furnace and the C terminal on the (new) thermostat. Then, to not confuse the next person, place the C labels that came with the thermostat at each end of the orange wire.
Additionally, is your "furnace" also an A/C? If it is just a furnace, you will only need to connect the Rh wire to the thermostat R. You will also likely not need to connect Y (this is used to call for cooling). The G wire allows the thermostat to turn on just the fan. W is the wire that tells the furnace to call for heat. R is the wire that supplies half of the 24vac current to the thermostat. The C wire is the other half of the AC current and is needed only if the thermostat requires power (as it does in the Nest case, but probably not in your Emerson which relied on batteries).
Hope that helps.
