Go buy a new thermostat and follow the directions in the package. The wires are pretty simple. R terminal is power, W is heat, Y is cool, G is fan, C is common. On a typical thermostat you will have all these with the exception of the C term. It will either be RC and RH with a jumper between them. Leave the jumper in if you don't have a 5 wire system. Make sure you lable your wires coming out of the wall because you don't want to have to open up the indoor unit to check them.
Answers & Comments
Go buy a new thermostat and follow the directions in the package. The wires are pretty simple. R terminal is power, W is heat, Y is cool, G is fan, C is common. On a typical thermostat you will have all these with the exception of the C term. It will either be RC and RH with a jumper between them. Leave the jumper in if you don't have a 5 wire system. Make sure you lable your wires coming out of the wall because you don't want to have to open up the indoor unit to check them.