We study superconductivity and superconductor-insulator transitions in extremely thin metal films and nanowires. We grow the thin films and nanowires in a dilution refrigerator under ultrahigh vacuum at cryogenic temperature and perform all the electronic measurements in situ. Since the samples never see ambient air and temperature, the method allows us to access monolayer thicknesses without worrying about oxidation, and examine the evolution of the electronic properties with increasing thicknesses, varying magnetic field, and incremental magnetic impurity densities, all on the same sample. The experiments have resulted in the surprising discovery of enhancement of superconductivity by parallel magnetic field in ultrathin Pb films.