The course takes its starting point in how we can understand how the Universe formed and evolved through the study of its contents and in particular the study of galaxies. Galaxies are mainly made of dark matter, but the light we observe comes from the stars, the baryonic-bright matter. Through the study of the stellar light emitted by the galaxies we can learn about the universe itself. Through these studies you naturally encounter Einstein's general theory of relativity and the Friedmann equations and their solution. We will go through the observational evidence for dark energy in detail. Dark energy is today thought to govern the evolution of the universe.