The digital pins on the Arduino are the ones that are used the most when connecting external sensors. These pins can be configured for either input or output. These pins default to an input state; therefore, when we are using a pin for input we do not need to explicitly declare them as input pins; however, it is good practice to do so because it will make it easier for someone reading our code to understand what the pin is being used for.
The digital pins will have one of two values: HIGH (1), which is 5V, or LOW (0), which is 0V. Once we start to program the Arduino, we will see how to read from or write to these pins.