This is the educational course inside the BOOSTalent project - «Density functional theory for computational materials design». This is the first course in a series on quantum mechanical calculations of materials. In this course, we will delve into the Density Functional Theory (DFT), a theory widely used for material property calculations in materials science, biochemistry, drug discovery, solar cells, batteries, and many other fields. This course is purely theoretical but crucial for proceeding to practical courses in quantum mechanical calculations