This is the first of a series of three lectures on the connection between matrix models and supersymmetric gauge theories recently proposed by Dijkgraaf and Vafa. I will review in this lecture many aspects of the low energy dynamics of $N=1$ and $N=2$ supersymmetric gauge theories (such as the calculus of the effective superpotential, the Seiberg-Witten solution, etc.) that will be important in the following lectures.