This circuit demonstrates a GPIO input with a pull-up resistor.
The GPIO pin is represented by the junction between the 10 kΩ resistor, the push button, the LED branch, and the voltmeter positive probe.
Watch the voltmeter: when the button is released, the GPIO pin is pulled up to 5 V and reads logic HIGH. When the button is pressed, the pin is connected to ground and reads logic LOW.
The LED is only a visual indicator. It turns on when the button pulls the GPIO pin LOW.
