It's an open-source physical computing platform based on a simple microcontroller board, and a development environment for writing software for the board.
For this workshop we worked in pairs, we were asked to follow a simple set of instructions by our tutor Jaap where we lit up the bulb.
We then went onto the arduino website and used a code which allowed us to manipulate the rate at which the bulb flashed.

Arduino is a tool for making computers that can sense and control more of the physical world than your desktop computer.