Complex sentence: Shōninki is called as the authentic manual of the ninja because it represents a basic guide for ninjutsu practicing, however the topics inside this book are only a brief introduction, they have to be explained by a master in order to transmit the whole knowledge.
Split into simpler sentences: Shōninki is called the authentic manual of the ninja because it represents a basic guide for ninjutsu practice. However the topics inside this book are only a brief introduction; they have to be explained by a master in order to transmit the whole knowledge.