What does Payout and Lay to Lose mean?

Payout: choose Payout instead of the Lay to Lose option if you prefer to specify a particular payout on a series of bets, as opposed to a bet by bet liability.

Lay to Lose: If you have a particular figure that you are willing to risk as a layer, you can enter this amount on the bet slip and the exchange will calculate the level of backers stake this equates to on your behalf.