The close relationship between charged particles and electromagnetic fields has been well known since the 19th century, thanks to James Clerk Maxwell's brilliant unified theory of electricity and magnetism. Today, electromagnetism is recognized as an essential aspect of human activity and has consequently become a major component of senior high-school and first-year university science curricula. However, while the action of electrical force on charged particles is generally well understood, that of the magnetic force still remains a mystery for some students, and thus the analysis of combined interactions quickly becomes a real puzzle. To improve the teaching of these phenomena, and also to facilitate comprehension by students, we have developed a computer-based simulator to replicate the motion of a real charged particle under the influence of any combination of electric and magnetic fields. Using this software, students are able to visualize the motion of charged particles and thus gain a better understanding of the effect of electric and magnetic fields. The software is available as a free download. (Contains 8 figures.)