The assignment of this master thesis was to investigate the software package XGSLab, a computer program for electromagnetic simulation for power supply, grounding and lightning protection. Its five modules are briefly described and an example of its use for the purpose of determining the optimal soil model from geoelectric sounding dada is given. The introductory chapter highlighted the importance of knowing the characteristics of the soil in which the earthing system is buried. The second chapter describes the electrical resistivity of soil and how its values differ depending on soil moisture, soil temperature, soil chemical composition, and geological characteristics. The third chapter describes the measurement of the apparent resistivity of the soil by geoelectric sounding methods. The arrangements of the electrodes and the manner of their spacing during the measurement are given, as well as the formula from which the apparent resistivity is computed from geoelectric sounding data. The fourth chapter describes the interpretation of geoelectric sounding data using the GEOS program, which is based on the comparison of resistivity transforms computed from geoelectric sounding data and soil model resistivity transforms. Chapter 5 briefly describes all the modules of the XGSLab software package. The first four modules include an SRA module that is used to interpret the results of geoelectric sounding. In the sixth chapter, the interpretation of geoelectric sounding data was performed using the software package XGSLab and using the program GEOS for two chosen examples. In the first example, the simulated geoelectric sounding data were interpreted, assuming that the current and voltage electrodes are point. In the second example, the real results of geoelectric sounding were interpreted. For simulated geoelectric sounding data, the XGSLab software package and the GEOS program give similar results, but this does not apply to the real geoelectric sounding data. This shows the lack of the XGSLab software package, which with a large error takes into account the influence of the depth of burial of current and voltage electrodes on the computation of the apparent resistivity.