Discounting future cashflows basically means taking into account that money promised in the future is worth less than the same amount of money promised now. The discount refers to the amount of value difference it would take for you to accept the future payment rather than payment now.
For example, if I offer you £100 now or £100 in a year, you would always choose to take it now. Why? Because inflation, money in the bank, things can change etc. So how much would I need to offer for you to think the payment in a year is better? £110, £120? £200?. That concept is the time value of money, and discounting future cashflows is a financial mechanism for taking it into account.
In this case, a contract promising £190k a week that has 24 months left might pay out £18m, but if you were offering to pay someone out of it you would pay it less with a full payment now. How much the discount is varies due to the circumstances. In this case a very cash rich person like a top level pro footballer is probably less in need of the cash now than say you or I might be, so will be more comfortable with receiving the amounts in the future. Therefore there time preference for money will lead to a lower discount being needed.