Future 5G communication systems require more demanding performances than the existing cellular communication systems, e.g., 10 to 100 Mbps user data rate and much larger cellular spectrum efficiency. The well-used multiple access methods like CDMA and OFDMA are hard to achieve these challenging requirements simultaneously even with advanced signal processing techniques and base station cooperation. Recently, massive MIMO has gain much attention since it provides large signal dimensions that can be used to improve future 5G cellular system performance. This tutorial paper describes a recently proposed multiple access scheme called multipath division multiple access (MDMA) based on massive antennas and multipath channel characteristics in millimeter wave band, which offers uniform user data rate and achieves high cellular spectrum efficiency for 5G systems. We describe the fundamental principle and show the uplink and downlink block diagrams, control signaling and the call setup process. Besides, benefits of using MDMA as a multiple access scheme are discussed. Finally, practical concerns are addressed for future research directions.