In simple terms the Arduino is a small computer that can be programmed to connect and control various physical objects.
There are two elements to the Arduino board – first is the hardware itself which is the microcontroller (the brain) and second is the software that you need to create and send a program to the Arduino. Arduino has a number of pins that can be either ‘input’ and receive data from items such as switches, buttons and sensors or set as ‘output’ and send data to control items such as motors, lights and sounders. This type of programmable development board is better known as a microcontroller.
You use the Integrated Development Environment (IDE) to create a sketch (program) that you upload to the Arduino board. The IDE is a very simple interface that runs on your computer and is available for Windows, MAC and Linux. The sketch tells the hardware what to do and is uploaded to the Arduino from your PC via a USB cable.
There are many types of Arduino out there but the book focuses on the most popular – the Arduino Uno.
Arduino Project Handbook 