Kalshi is a CFTC-regulated exchange where every contract asks a yes/no question about a future event. You buy YES if you think it happens, NO if you don't. Price = market-implied probability.
When the event resolves, the winning side pays $1.00 per contract. You profit the difference between your fill and $1.00.
Minimum to start? You can begin with a small bankroll; size by fractional-Kelly, not all-in.