Start here. This is the direct spoken answer to practice first.
Overview
RAG is useful when an answer needs evidence that is private, current, or too large to place permanently in a model.
Retrieval-augmented generation first searches an external knowledge source for evidence relevant to the request, then gives selected results to the model as context for its answer. It changes the request at runtime rather than retraining the model. The application still owns retrieval quality, permissions, citations, validation, and the decision to abstain when evidence is insufficient.