This lecture introduces the concept of differential equations, discussing their definitions, properties, and methods of resolution. The instructor explains the relationship between a function and its derivative, emphasizing the search for solutions to these equations. Several examples illustrate the nature of differential equations, including their graphical representations. The first example demonstrates a simple equation where the solution is expressed in terms of a constant. The second example explores a more complex equation, highlighting the existence of multiple solutions and the implications of division by zero. The third example presents a cubic root function, revealing the existence of three families of solutions. Throughout the lecture, the instructor emphasizes the importance of understanding the qualitative and quantitative properties of differential equations, including existence and uniqueness of solutions. The lecture concludes with a preview of future topics, including methods for calculating solutions and further exploration of existence and uniqueness results.