Digital technologies/Arduino/Arduino- Beginner/Introduction to Sensors
Sensors enable the microcontroller to sense the surrounding environment. Many sensors exist on the market, including but not limited to buttons, temperature sensors, pressure sensors, photoresistors, humidity and moisture, and many more. The output of the sensor (a voltage) changes based on the measured environment properties, and sends that signal over to the Arduino board.
Different sensors will use different voltage levels and different methods of communication with microcontrollers. It is always important to read their datasheet and make sure they are compatible with your system before continuing or design your system around the sensor specifications.