Résumé : In the last lecture I will apply the macroscopic fluctuation theory to solve specific problems. I will show that several features and behaviors of non equilibrium systems can be deduced within the theory. In particular I will discuss the following issues: the presence of long range correlations in stationary non equilibrium states; the explicit computation of the large deviations rate functional for a few one dimensional stationary non equilibrium states; the existence of dynamical phase transitions in terms of the current flowing across the system, the existence of Lagrangian phase transitions.