I purchased a non-programmable digital thermostat to replace an analog thermostat with wiring red, white yellow and black.

How do I match the wiring?
HELP!!

What letter and color was connected on the old thermostat? What is the model number of your new thermostat?

Chances are, red to RH &RC, white to W, yellow to Y, and black to G. You might look at the furnace and see it that is the way they are connected there.