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.）
More information
——How to wiring a 4 pin push button switch
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