The paper describes the creation of modelling and simulative tool of Petri nets by means of which it is possible to simulate processes and it enables a vast tool support in the fields of model check, graphically oriented simulation and software verification. The advantage of process modelling with Petri nets is their formal description, which refills the graphical display. There are numbers of editors and tools for Petri nets modelling and simulation on the market. By the use of the created simulation tool of Petri nets it will be possible to model and simulate and consequently to form the processes running on the systems. The important aims of the designed tool is to create, model and visualize processes in the operating systems of PC, to create appropriate models which optimize progress in educational processes and to implement IF-THEN rules into modellig processes. The first part is concerned with the definition of the basic terminology from the fields of modelling, the principles of modelling and simulation, and the basic features of Petri nets. The implementation of forming into Petri nets tools has given a strong tool to model real processes. By means of the created tool it will be possible to model and simulate the processes in operating systems, educational processes in LMS and possible to model IF-THEN rules, or fuzzy Petri nets.