The Mahou Galaxy RPG functions like many other tabletop RPG's do. A group of participants get together to create a story about characters in the given setting while utilizing game mechanics to make things interesting.
One participant is designated as the "Game Master" (GM) and all others are "Players". Each Player controls a "Player Character" (PC) that they probably made using the system's Character Creation rules, while the GM develops and controls the world and "Non-Player Characters" (NPC) that the PC's interact with. The GM presents challenges for the PC's to overcome and are awarded Experience Points (XP) based on the difficulty of the challenge and the degree of success (or failure). PC's have a variety of means to overcome challenges, including Stats and Skills, Racial Abilities, Facet Abilities, Spells, and old-fashioned ingenuity.
Gameplay consists of campaigns, sessions, and scenes. A campaign is an over-arcing storyline or set of scenarios that make up the total game experience. A session is a period of play a series of events