How to design a circuit ?

Question

i can only use an optical amplifier, thermistor, green and red LED, resistors. the red LED should light up when subjected to ambient light while green LED should light up when subjected to dim light

Answer 1

Perhaps you mean you have an "operational amplifier".  If that is the case, you make a stack of LEDs and resistors between your voltage supply, with each LED in series with its own dropping resistor (red LED, resistor, resistor, green LED).  Connect the center point of this stack to the output of your op-amp.

The (-) input of your op-amp is connected to a voltage divider made up of two resistors.  The (+) input of your op-amp is connected to a voltage divider made up of a resistor and your thermistor (assuming your thermistor has light-sensitive properties).

That should give you what you need.