I will briefly outline basic concepts of the stellar atmospheres theory. After summarizing basic structural equations describing a stellar atmospheres, an emphasis is given to describing efficient numerical methods developed to deal with the stellar atmosphere problem, namely the method of complete linearization ant its recent variants, and the whole class of methods known by name Accelerated Lambda Iteration. In the next part of the lectures I will briefly summarize existing computer codes, with an emphasis on our code TLUSTY, and list some of the most useful grids of model atmospheres that are publicly available. Next, I will show how the model atmospheres and synthetic spectra are used in quantitative stellar spectroscopy in order to determine basic stellar parameters and chemical abundances. Finally, I will briefly describe an application of model atmosphere theory and models to related objects, such as accretion disks around various accretors, and atmospheres of substellar-mass objects - extrasolar giant planets and brown dwarfs.