The topic of reference frames, which is taught at an early stage of secondary school physics is quite challenging for students. The two main reasons behind this are the high level of abstraction required and the lack of understanding of the vector nature of velocity. In the paper we introduce a method we use successfully in teaching reference frames with our students and which is based on computer simulations. We use a new simulation program, called Fizika, which is developed by a Hungarian team and is available for all science teachers for free. Through the simulations and graphs of motions, we investigate different stationary and uniformly moving reference frames and introduce the concept of relative velocity. With the help of the simulations we can provide our students experimental experience, on which they can build with much more confidence and which will lead them to a deeper understanding. The simulations can also be used for extracurricular lessons with talented students, since the program can also be used to investigate complex motions and their graphs.