I you want to make this simple flip-flop circuit you need some electronic components below;
* 2x 470ohm ressitor
* 2x 100k ohm resistor
* 2x BC547 NPN type BJT transistor
* 2x 10uF/25V capacitor
* 1x Green LED
* 1x Red LED
Description: The led's color is not essential you may use diffirent colors such as yellow, blue, white etc. 100k ohm valued resistor and 10uF valued capacitor determine blinking time interval of LEDs. Simply the time of blinking is determined by T = R x C = 100k x 10u =1s. If you change the value of resistor to 10k you will see the blinking interval time approximately 0.1s because of T = R x C = 10k x 10u = 0.1s. If you change the value of capacitor to 1uF you will see the same result because of T = R x C = 100k x 1u =0.1s.