A bet: you say what will happen ("Milan win"), you put money on it (the stake), and the bookmaker names a price (the odds). Right → you get stake × odds back. Wrong → the stake is gone.

Odds 2.50 means: 10 CHF becomes 25 CHF (15 profit) if you are right. The higher the odds, the less likely the bookmaker thinks it is.

Odds hide a chance: 1 ÷ 2.50 = 40%. Bookmakers price every outcome a bit too low so the chances add to more than 100%. That extra is their margin. You can change the odds format (decimal, fractional, American) in the ◐ menu.