3-pin push button switch is a relatively common type of push button switch. Usually, it only has the function of a button and does not have the function of an LED indicator.
Taking ONPOW 3 pin push button switch as an example. 
Usually, only two of the three pins are used unless you have a more special need. When you use the "COM" and "NO" pins, the push button switch forms a normally open circuit. When the push button switch is pressed, the device it controls will start (here we do not consider the difference between the self-resetting and self-locking functions of the push button switch). When you use the "COM" and "NC" pins. The push button switch forms a normally closed circuit, and the device it controls will only be turned off when the button is pressed.
（Let's take the following circuit diagram as a reference. When you connect the device and power supply with the COM pin and the NO pin, and press the push button switch, the light will turn on.）
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