It is known that for the study of continuous dynamical systems the discret case plays an important role because, with it we can study the continuous one by using the Poincaré return map. In the discret case we can distinguish between conservative maps (or area preserving maps, in the case of flows living on a 3-dimensional manifold) and non conservative maps. Among the last ones, there are the dissipative maps. Two of the main subjects of the study of dissipative maps are: the existence or not of attracting periodic orbits and the possible existence of strange attractors -that is, attractors that are neither periodic orbits nor invariant curves, which are minimal and contain a dense orbit. Moreover, these attractors can have sensitive dependence on the initial conditions, or have an absolutely continuous invariant measure. On the other hand there exists a transition between these two behaviours: the so-called flip or period doubling bifurcation cascade. After the final of this cascade (in a suitable set of parameters), strange attractors can appear, and also more attracting periodic orbits.This doctoral dissertation is divided in four chapters:In the first one we study the dynamics of the so called logistic map; more specifically, we study first fold and flip bifurcations of this family, giving analytical expressions of the parameter values for which they occur. In the second chapter, we consider the Hénon map with strong dissipation. In the third chapter we study the Newhouse phenomenon. To this end we prove a more complete version of the phenomenon than others proved before, in which we show the existence of generic saddle-node and flip bifurcations, for parameters close to the parameter of homoclinic tangency. In chapter four we study the behaviour of the codimension one and two bifurcations in one and two dimensional families of maps. To do this, we consider one-parameter families of diffeomorphisms, to study saddle-node and flip bifurcations, and two-parameter families of dissipative diffeomorphisms, to study cusps and codimension two flips.