Retrieval Augmented Generation (RAG) combines user prompts with relevant external information to create expanded prompts for large language models, enabling more accurate and timely responses. This comprehensive guide covers the fundamentals of RAG implementation, including vector search, embedding models, and step-by-step processes for data preparation, retrieval, augmentation, and generation. RAG addresses key limitations of LLMs such as hallucinations and lack of access to proprietary information by providing contextual external data. The guide explores practical use cases including question-answering systems, customer service, content generation, and code assistance, while also covering evaluation methods and integration with other modeling approaches.