This tutorial provides an introduction to equilibrium electrochemistry related to electrode potentials and their applications. The origin of electrode potentials from the point of view of the foundations of thermodynamics is considered and it is shown how their value can be used to find important chemical data: equilibrium constants, changes in free energy, enthalpy and entropy during transformations in chemical reactions, activity coefficients, selective ion sensitivity. The emphasis is on understanding the essence of the phenomenon and its application to chemical tasks. The mathematical aspects of the subject are minimized to preserve the utmost clarity of presentation. The manual is designed for junior students studying chemistry or related disciplines.