The PEPSY-QNS (Performance Evaluation and Prediction SYstem for Queueing NetworkS) was developed in the 90’s at University of Erlangen. It has a very simple and user-friendly interface. So far there has been more than 50 analysing methods built in the system.\parPEPSY-QNS consists of the basic system -- so called PEPSY -- and the graphical XPEPSY. PEPSY consists of three parts that were designed to fit together. This paper demonstrates using of PEPSY on queueing networks and handling different system files eg. input and output data. \parAn example has been given for calculating the main system characteristics such as throughput, utilization, average response time, average waiting times etc.