D3.js is a JavaScript library that enables the creation of interactive graphs and charts, including visually appealing bubble charts, which are circles whose sizes correspond to data values. The tutorial guides users through building a static bubble chart using D3.js's pack layout and then making it dynamic with real-time JSON data from PubNub Data Streams. It emphasizes the importance of binding streaming data to update and animate the chart dynamically, using the enter, update, and exit pattern to manage data nodes effectively. The tutorial also covers creating smooth transitions between data updates, ensuring a seamless animation effect by utilizing D3.js's functionalities to modify the appearance and movement of bubbles in response to data changes. It provides access to a demo and source code on GitHub for further exploration.