The chemical composition of the Sun is the foundation of astronomy. Its knowledge greatly helps us to understand the solar interior, evolution and the entire solar system in general because all cosmic bodies are essentially made of the same chemical components. The methods used for this purpose, and which will be described in this paper, are solar (absorption) spectroscopy and mass spectroscopy of primitive meteorites. Absorption spectroscopy of sunlight gives a certain spectrum full of absorption lines. Each individual element, in other words its atom, has its characteristic "imprint" in the obtained spectrum. The spectrum of an atom of a certain element is a representation of its atomic structure and it is composed of a series of dark spectral lines specific to a particular atom. In this way, one can conclude about the chemical composition of the Sun and its atmosphere and this is precisely the basis of spectral analysis. Traditionally, solar spectroscopy was performed in 1D models of the atmosphere with some simplifications, but today more and more sophisticated and realistic 3D models are used, which gives better results, so the previous ones need to be corrected. Mass spectroscopy is performed in adequate laboratories, in which the chemical composition of a particular body, here a meteorite, is determined with very high precision. The most primitive meteorites are analyzed, and the abundances of the elements obtained serve as an excellent comparison with the abundances obtained by solar spectroscopy. The chemical composition of the solar atmosphere is not equal to that of the sun. Namely, there are significant deviations and this is primarily caused by a very high temperature jump between the lower and upper part of the atmosphere. The abundances of the elements change depending on their first ionization potential (FIP), which will be shown in further work.