Polkadot is like any other cryptocurrency traded on so called exchanges, which determine the price through supply and demand. Polkadot's price is both highly volatile, and closely correlated with broader trends in the market. If bitcoin rises or falls, then you can expect a similar move in the price of DOT. We should note also that DOT is a relatively young
currency, which points to extra volatility as technical challenges arise and are overcome (or not
There are hundreds of projects using the Polkadot network, whose popularity (or lack thereof) will
influence the perceived longevity, and therefore trading price, of the token.