Three major unresolved issues in modern Astrophysics are the origin of the initial mass function of stars and it potential universality, the nature and interplay of physical processes that regulate the star formation rates and efficiencies in star forming molecular clouds, and the origin of turbulent motions in the clouds and in the interstellar medium. Over the last two decades, the effects of physical processes such as turbulence, magnetic fields, and stellar feedback on the structure and dynamics of molecular clouds have been modeled. However, a global analysis that incorporates all of these processes in a single set of simulations is still missing. The aim of this project is to provide a complete picture of the entire life cycle of molecular clouds that form and evolve in different galactic environments. Using high resolution numerical simulations, I will model the formation of molecular clouds from converging flows in the atomic phase of the ISM, the fragmentation of the clouds and the formation of stars within them, and the ways feedback from the newly formed stars impacts the dynamics of the clouds and leads to their dispersal. In additiona to exploring a large variety of galactic environments characterized by different gas-phase metallicities and magnetic field strengths, the simulations will include novel aspects such as the coupling of a state-of-the art magnteohydrodynamical code (RAMSES AMR code) with a state-of-the-art stellar evolution code (MESA code). This will allow me to follow very accurately and self-consistently the effects of feedback from massive stars on their parental molecular clouds. The results from this large set of simulations will allow me to evaluate the dependence of the shape of the IMF and of the star formation rates and efficiencies on the environment. I will also be able to quantify the contribution of massive stars on driving turbulent motions in molecular clouds and in the ISM.