How do I wire this thermostat?
You're going to have to take a look inside the furnace, where you should find the control board where all these wires terminate. Each terminal on the control board should be labeled, so just make a list of letters and colors. Then go back to the thermostat, and use the list to connect the wires to the proper terminals.  

If you post the make and model (model number would also help) of the furnace, or a quality picture of the furnace wiring diagram (should be printed on the inside of the access panel), somebody may be able to offer a better answer.