The guide provides a comprehensive walkthrough on implementing authentication and authorization in a Next.js application using Supabase and Permit.io. It outlines the process of setting up Supabase for email-based authentication, managing user roles through Relationship-Based Access Control (ReBAC), and enforcing policies using Supabase Edge Functions and a local Policy Decision Point (PDP). The tutorial focuses on building a real-time polling app where users can create polls, vote, and manage their content, emphasizing the importance of defining clear access control policies to manage permissions effectively. It demonstrates how to integrate Permit.io to define and evaluate authorization logic, ensuring that actions like voting and poll management are restricted based on user roles and relationships, such as preventing creators from voting on their own polls. This setup provides a scalable foundation for applications requiring detailed authentication and authorization mechanisms, combining Supabase's backend features with Permit.io's flexible access control model.