The aim of this tutorial is to present basic results (e.g., on controllability, observability, feedback laws...) in control theory of systems modeled by ordinary differential equations. First, we give the classical results for linear control systems. Then, we give the direct applications of this linear theory to local results for nonlinear control systems. Finally, we present some more advanced tools to deal with global properties and with the case where the linearized control system is not controllable. We illustrate the methods presented on simple physical systems.