My furance is running but no heat is blowing out of vents. Help!!

My furnace is running but no heat are coming out of vents.

My furance will turn on but there no heat. An there's a little green light I can see threw the furnace window the light does not stay on it blinks. What's going on

Inside the blower door should be a key to the blink code. Sometimes the blink code is on the control itself. These lights usually blink x times, pause, blink x times, pause, etc.
Before removing the door, count the blinks between pauses. An example would be blink, blink, blink, pause, blink, blink, blink, pause. That would be a '3' or '33' code depending upon the control.