The far left push button is used to turn on the output. The output (orange) will remain on for ~20 ms before turning off as long as the on button is pressed for more than 20 ms. (realistically this is a near instantaneous press of a button for a human operator). After the output has turned off, the circuit must be reset by pressing the other two push buttons several times to dissipate the voltage within the circuit and reset for another press of the on button. correct me if I'm wrong but these could be replaced with resistors on the order of a couple mega ohms each in an actual circuit.
