Yugi gets a millenium piece from his grandpa, and his grandpa also introduced him to a card game called Duel Monsters! Anyway Pegasus takes his grandpa's soul and Kaiba takes his grandpa's Blue Eyes White Dragon card.. anyway Pegasus ends up trapping Grandpa's soul in a card and if Yugi wants to save him he must enter a tournament and defeat him, and with defeating him he would also be given the ultimate champion name of duel monsters etc.. Anyway he brings his friends along for the journey and they meet many enemies that they must defeat and Yugi learns strategies that he uses as he duels and so does his friends.. his millenium piece allows him to use an ancient spirit to guide him through the game..later on there is more then that but it's not my job to tell you *everything* about the series Xp