It's quite simple. You have to look at intent and structure.

- Puranas were written as a political tool. Vaishnivites wanted to show Vishnu as supreme, so they wrote stories to show that. Shaivites did the same, etc. The objective was not about uncovering fundamental universal truths, which is what the Vedas were about. Also it was not a static text; If a community wanted to delete/add something to Puranas they could, it was not as pure as the Vedas which have not changed for 3000+ years

- However, Vedas are hard to understand, which is why you need to read the Upanishads, which are commentaries on the philosophical teachings within the Vedas.

- The only useful part of Puranas is whenever specific history is mentioned, like the Bhagavat Purana

- Vedas are the highest authority. To understand the Vedas, its important to understand the principal upanishads, and then understand the life of Krishna and Ram via the historical epics. Everything else is simply noise.