The theory of branching processes offers a mathematical model for the study of populations in which individuals live, reproduce, and die independently of one another. In this chapter, we begin with studying the Galton-Watson process, the simplest branching process. Then, a generalization of this model is presented, allowing individuals to have offspring of different types. Subsequently introduces the continuous-time branching process and studies some of its properties. A model is developed with two types: infected and asymptomatic, to determine the expected number of individuals infected with Covid 19 in the city of Bogota.