Doraemon and Nobita were using special shoes that allows them to jump into the worlds of the books that they want. Nobita let Shizuka use those shoes to enter the world of the book that she wants. Shizuka got lost in one Nobita's Sinbad Legend of the Seven Seas book. After Nobita's mother burned all of his books, Doraemon and the others must find another way to save Shizuka. Source: ANN