Most of the present-day Hinduism is directly or indirectly based on the legends written in the Puranas. It is a vast collection of ancient literature (originally written in Sanskrit) covering a wide range of subjects, especially the stories of the various gods and deities in Hinduism.
The Puranas were composed in the post-Mahabharata period. Because not all the sections of the Puranas were written by a single person, we often find some instances in them that are quite contradictory to each other. This eventually gives the critics an opportunity to point out and propagate how unscientific the entire Hindu literature is.
However, the truth is far from it. The original Puranas were also rewritten and possibly diluted several times during Islamic rule in India, and thus they do not hold the same authority as other texts like the Vedas and the Upanishads have over Hinduism.
Anyhow, there are a total of 18 Mahapuranas (or, major Puranas) and 18 Upapuranas (or minor Puranas). Each Purana is composed in praise and glory of a specific deity.
For example, the Shiva Purana contains the legend of Lord Shiva (the Hindu god of destruction), while the Bhagavata Purana tells how Lord Vishnu plays an important role in maintaining and balancing the dharmic laws of the universe.
Names Of 18 Puranas (PDF Download Links)