The Arduino Yun is a single-board computer that can be used to build various projects, including a photo booth. The project involves connecting a webcam to the Arduino Yun, uploading images to Dropbox using Python, and triggering these actions with the press of a button. To achieve this, the user needs to install specific libraries and drivers for the webcam and Dropbox API, as well as write code in both the Arduino programming language and Python. The final result is a photo booth that can take pictures, upload them to Dropbox, and trigger these actions with a single button press.