This lecture covers the numerical resolution of groundwater flows using finite differences, focusing on the discretization of Laplace's equation in 2D for steady flows. It explains the need for numerical resolution due to complex geological boundaries, heterogeneous soil nature, and transient flows. The lecture demonstrates the finite difference method with Excel, discussing the discretization of the domain, Laplace's equation, and boundary conditions. It also provides a step-by-step procedure for solving flow problems under a dam. Practical examples with Excel are shown, emphasizing the importance of interactive calculations and graphical representation of results.