I have a pontiac montana 2000 my problem is i dont have warmth in front of in my heater and behing it is very warm

There are a couple of possible problems Carole.
First one is there may be a blockage inside the heater core causing poor flow of the coolant from the engine which gives you the heat.
If this is the case the core will need to be flushed out or possibly replaced.
Second problem may be the door that is supposed to move inside the heater box that changes the air flow from cold to hot may not be working properly. The controls may be defective or the door is seized.
Because your heater in the back is working well the thermostat and the coolant level should be OK.