Most of what a person coming into yoga encounters of the tradition comes through the Purāṇas. The stories of Kṛṣṇa’s childhood, of Hanumān leaping to Lankā, of Gaṇeśa receiving his elephant head, of the goddess slaying Mahiṣāsura. The festivals observed through the year, the deities on the altar, the fasts of Ekādaśī and Śivarātri, the accounts of pilgrimage places, the descriptions of the four yugas and the avatāras of Viṣṇu: the Purāṇas are where this material lives and where it has been carried for centuries.
The English word applied to them is “mythology.” This places the Purāṇas alongside the Greek and Norse mythologies sounds culturally valuable but not held as true by anyone. This is not what the Indic tradition has ever said about them.
The word itself
Purāṇa comes from purā means ancient, from before. The word itself appears in the Vedas. The Atharva Veda (XI.7.24) names Purāṇan alongside the ṛc and the sāman. The Chāndogya Upaniṣad (7.1.2) and the Bṛhadāraṇyaka Upaniṣad (2.4.10) both place Itihāsa-Purāṇa as the fifth Veda. The Purāṇas are not outside the Vedic corpus. They are part of it, in a different form.
Prabhu-Saṃhitā and Suhrit-Saṃhitā
Swami Sivananda, in All About Hinduism, draws a distinction that is useful here. He calls the Vedas Prabhu-Saṃhitās (commanding treatises), the speech of a sovereign. The Itihāsas and the Purāṇas he calls Suhrit-Saṃhitās (friendly treatises), the speech of a well-wisher. This is not a classical śāstric category from a primary text. It is his articulation, and it names something real about how these two bodies of literature operate. The Vedic mantras command the ritual. They instruct and prescribe. The Purāṇas convey the same dharma through narrative, the life of a king, the fall of a sage, the descent of an avatāra. The listener receives the teaching through attention to a story rather than through ritual injunction. Both carry the same knowledge. They address it to different capacities of reception.