[SwSwinger]

I work at YugaByteDB as a software engineer, and I encounter people in your situation regularly. You are asking HN for product-market fit basics on something that is more like a tool or innovation than an end-to-end company. If you join a growing startup (Series C+) related to the product area you like, then you'll be able to understand how that market works from the default company culture. You'll also be able to pitch your own product ideas of similar scope - if the company isn't too established - after the first year or so when you understand their focus more deeply.