Arduino generally refers to the open-source platform or company by the same name. The Arduino platform is comprised of circuit boards, software, and an IDE for writing code. The boards are inexpensive and can perform a variety of basic functions from controlling an LED to manipulating servo motors.
Arduino microcontroller boards can send and interpret signals for a variety of hardware. You can use an Arduino to control servo motors, relays, buttons, LEDs, and more.
The Arduino Uno needs either a 5V USB connection or a 7-12V DC power adapter to operate. You can also power the board using the 5V and 3.3V pins, but it isn't recommended.
Programs are created in the Arduino IDE using a language called Processing. The programs are exported to files known as sketches. Sketches are then loaded onto the Arduino by connecting it to the computer with the IDE.
The Arduino IDE includes a Library Manager. Open the IDE software then navigate to Sketch > Include Library > Manage Libraries... This will open a list of currently installed libraries and ones available for install. You can read more about this process on the official Arduino website.
The best way to control a relay with an Arduino is to use a relay module. These boards provide pins that are easy to connect to the Arduino. These boards can be wired into a circuit as needed.
Most Arduino boards support a maximum of 12 servos. The Arduino Mega boards support up to 48 servo motors. Need to control more? You'll need more Arduinos.
Arduino provides instructions for burning the bootloader on an Arduino. You will need an in-system programmer to burn the bootloader. Once you have the necessary hardware, the tools you need are part of the Arduino IDE under the Tools > Burn Bootloader menu.
LCD screens connect to the Arduino using the input/output pins. The screen itself can be controlled using the Liquid Crystal library. Install it from the Library Manager in the Arduino IDE to get started.