This lecture covers the theory of free groups, focusing on their definitions, properties, and the relationships between free groups and other algebraic structures. The instructor begins by discussing the concept of free groups and their generators, emphasizing the importance of understanding morphisms in the category of groups. The lecture illustrates how to construct a free group from a set of generators and how to determine the relationships between these generators. The instructor provides examples to clarify the concepts, including the construction of homomorphisms and the identification of kernels. The discussion extends to the notion of quotient groups and the significance of normal subgroups. The lecture concludes with an exploration of the universal properties of free groups and their applications in group theory, including the construction of free products and amalgamations. Throughout the lecture, the instructor encourages questions and interactions to ensure comprehension of the material presented.