The paper basically describes the gas turbine, together with its constituent parts; compressor, combustion chamber and turbine. Their role is described, as well as their basic constituent elements and structural designs. Each of the three standard gas turbine processes, open cycle, closed cycle and Brayton cycle with regeneration, is also detailed in the paper; and lubrication system and fuel system. As an introduction to the main topic, a general explanation of turbines as machines and their historical development is given. Along with the descriptions of the processes themselves, corresponding diagrams are attached, important for understanding how the system works. The main parts of the turbine are supported by pictures on which the parts are marked with the associated names. Ways to improve fuel quality are listed, as well as the consequences of unwanted elements in fuel. The aim of this paper is to explain the principle of operation of turbines and their importance in the world of mechanical engineering and maritime industry.