No single factor sets Bitcoin's price — it's a mix. On the supply side, new coins are issued on a fixed, shrinking schedule (cut in half roughly every four years at the "halving"), and the total is capped at 21 million.
On the demand side, prices respond to adoption, big buyers entering or leaving, regulation, macro conditions like interest rates, and plain market sentiment — fear and greed move prices fast in a 24/7 market.
For beginners, the takeaway isn't to predict these forces but to understand that short-term price is noisy and driven by many things at once. That's why disciplined approaches like dollar-cost averaging exist. This is educational information, not financial advice.