Connect the Q output of the D flip flop to one of the inputs of a two-input exclusive OR gate. Connect the other input of the exclusive OR gate to the voltage supply that you are using to power your D flip flop. Connect the output of the exclusive OR gate to the D input of the D flip-flop.
Connect one end of a 1,000 ohm resistor to the Q output pin of the D flip flop. Connect the other end of the resistor to the anode of an LED (light emitting diode). Connect the cathode of the LED to the negative terminal of the power supply.
Connect a frequency generator to the clock input of the D flip flop. Set the frequency generator so that it produces a square wave that has a high level and a low level voltage that is within the specifications of the digital logic you are using (most often 5 Volts and 0 Volts or 3 Volts and 0 Volts). Set the frequency of the square wave anywhere between 1 and 3 cycles per second.
Turn on the power to the circuit. Observe that the LED turns on and off at a rate that is about one half of the clock frequency applied. If you apply a 1 Hertz signal to the clock input, the LED would turn on for one second and then stay off for one second (will toggle the LED on and off).