Prompt engineering is the process of structuring words that can be interpreted and understood by a text-to-image model. This prompt book by OpenArt aims to help users learn essential building blocks and techniques to master Stable Diffusion. The book emphasizes the importance of a well-written prompt consisting of modifiers and good sentence structure, as well as well-adjusted Stable Diffusion parameters. The book also introduces the prompt format and various modifiers and magic words that can be used. The goal is to help users bring their creative dream images to life.