We have come a long way and mastered complex scenarios in the use of LLMs. This book focuses on practical application, so we did not delve deeply into the internal structure of the models. However, to develop advanced solutions based on LLMs, it is important to understand how they work. In this chapter, we will examine the inner workings of the transformer architecture and analyze its operation through concrete examples. You will see what formed the foundation of the breakthrough in Natural Language Processing that ultimately led to the creation of LLMs.