Odds work in football just like with any other type of bet you place. However, they can be shown in many different ways. For example, a 1/1 bet where you win 1 for every 1 you bet can also be shown as a multiplier 2.00. In the odds shown the first number is always how much you win, and the latter is how much you need to bet to win the first number.
For example, with odds of 3/1 you win 3 for every 1 you bet, so with a £10 bet you would win £30. However, you must also remember that with a winning bet your stake will also be returned to you, so in fact you get £30 in winnings + your £10 stake back = £40.