A negative trigger pulse(button press) at pin 2 turns off a transistor in the first 555 timer that otherwise shorts the capacitor(2.2uF) to ground. The output then goes high as this capacitor charges through the resistor(1M). When the charge on the capacitor is 2/3 Vcc, the 555 timer discharges the capacitor to ground. The output then goes low which starts the same sequence of events in the second 555 timer. The timing cycle of each timer is controlled by adjusting its resistor and capacitor(t = R1 X C1).
