The textbook presents the Kon-Sham theory (density functional method), which underlies modern calculations of electronic properties of condensed systems. The manual describes in an accessible form the basics of the density functional method; discusses the dynamic generalization of the method; gives an introduction to the method of quantum molecular dynamics and describes the application of the density functional method in the theory of superconductivity and the theory of magnetism. Numerous examples are given showing the results of the use of advanced formalism in the study of multielectronic effects in low-dimensional systems.