Server-Side Rendering (SSR) for React involves running React on the server to generate a page's initial HTML, which is then enhanced on the client side for interactivity. This process is beneficial for search engine indexing and reducing application complexity, particularly when using frameworks like Next.js that simplify SSR setup. The text provides detailed instructions on implementing SSR with Next.js, including fetching data with `getServerSideProps` and using Clerk for authentication. Clerk's integration with SSR allows for user authentication and data retrieval, such as user IDs or JWT tokens, before rendering a page. Additionally, it enables full SSR mode, which allows retrieval of the complete user object, offering functionalities like accessing a user's primary email address. The text encourages developers to explore further resources for integrating authentication quickly through Clerk's Next.js support and offers community support via platforms like Discord and Twitter.