"Building a Second Brain" by Tiago Forte is a guide to organizing your digital life and enhancing your creativity. The book introduces a system called CODE (Capture, Organize, Distill, Express) to help you manage information overload and make the most of your digital tools. Here are the key points:

1. Capture: Collect ideas, notes, and inspirations from various sources.
2. Organize: Sort and categorize the captured information in a way that makes it easy to retrieve.
3. Distill: Refine and summarize the information to highlight the most important insights.
4. Express: Use the distilled information to create and share your own content.

Forte emphasizes the importance of building a personal knowledge management system to unlock your creative potential and improve productivity. The book is filled with practical tips and real-life examples to help you implement the system effectively.