This chapter is under construction
Pins names are according to the diagram below.
Ignoring the Pi for a moment, one of the simplest electrical circuits that you can build is a battery connected to a light source and a switch (the resistor is there to (limit the current flow) and protect the LED):
When we use a GPIO pin as an output, the Raspberry Pi replaces both the switch and the battery in the above diagram. Each pin can turn on or off,or go HIGH or LOW in computing terms. When the pin is HIGH it outputs 3.3 volts (3v3); when the pin is LOW it is off.
Here's the same circuit using the Raspberry Pi. The LED is connected to a GPIO pin (which can output +3v3) and a ground pin which is 0v and acts like the negative terminal of the battery : (the resistor is there to limit the current flow and protect both the LED and the Raspberry CPU). A value of 1 kOhm will retrain the current around 1.5 mA