Outcome shares and fixed payouts
Mechanically, a prediction market for a yes-or-no event typically issues two kinds of outcome shares, one representing 'yes' and one representing 'no'. When the event resolves, shares on the correct side become redeemable for a fixed value, commonly 1 unit of whatever currency backs the market, and shares on the wrong side become worthless. Before resolution, both kinds of shares can be freely bought and sold, and their prices move as new information and trading activity shift the market's collective probability estimate.
A useful mental model is that a full set of 'yes' plus 'no' shares is always worth exactly the fixed payout amount together, since exactly one side will end up correct. That constraint is what ties the price of 'yes' shares and 'no' shares to each other, if 'yes' trades at 65 cents, 'no' should trade close to 35 cents, because together they must equal the full payout once the outcome is known.