There are fourteen types of learning or Vidyas – four Vedas, Six Vedangs, Meemansa, Nyay, Puranas and other religious scriptures. These fourteen learning along with Ayurveda, Dhanurveda, Gandharvaveda and Arthashastra becomes eighteen. All these eighteen learning’s originate from lord Shiva.
Lord Shiva created lord Brahma to felicitate the process of creation and bestowed him with all these eighteen learning’s. He also empowered lord Vishnu to protect the creation.
The four Vedas emerged from the mouth of Lord Brahma, on the basis of which were created the numerous scriptures like Vedangs etc. Since these Vedas were difficult to understand, therefore lord Vishnu took incarnation of Vyasa and created the Puranas, so that they could be understood easily. The Puranas contain four lakh shlokas and they help us to understand the essence of the Vedas.