The Puranas are a group of important Hindu religious texts, which are important to the Jains and Buddhists as well. They consist of narratives of the history of the Universe from creation to destruction, genealogies of the kings, heroes, sages and demigods, and descriptions of Hindu cosmology, philosophy and geography. See also Puranas.
The different Puranas usually give prominence to a particular deity and most use an abundance of religious and philosophical concepts. They are usually written in the form of stories related by one person to another.
They were exclusive teachings, the study of which were only allowed to the castes which were twice born. Anyone of the lower castes were subject to death if they were discovered to be reading them. The lower castes were also not allowed into the Mandirs to have Darshan of the statues or Murtis of the many Gods of the Hindu Pantheon.
The Gurus were well aware of the Puranas and could argue their points as well as any Rishi, but they did not believe or give any importance to the world of Gods and Goddeses they spoke of.
Guru Gobind Singh is known to have been a scholar of the Vedas and the Puranas. He used them to teach and educate his devotees in resisting the powerful men who sought their destruction, but he did not see them as having any part in or importance to Sikhism.
- See Wikipedia article on Puranas for more information