In this chapter, we present the basics of the physics and phenomenology of FGKM-type stars. This review is based on recent developments in the observational and theoretical domains of stellar physics, including a variety of techniques – spectroscopy, interferometry, photometry and large-scale stellar surveys. We focus on the advances in radiative transfer modelling and spectroscopy of stars across the full metallicity range. To provide the reader with the essential supplementary information, we also give a brief qualitative account of the structure and evolution of low- and intermediate-mass stars and of stellar nucleosynthesis. We also provide a brief overview of new models of stellar atmospheres and stellar spectra, with emphasis on non-LTE and hydrodynamics. Lastly, we discuss some of the relevant observational studies of stellar abundances in the context of stellar populations, evolution of metal-poor stars and Galactic archeology.