Wagering requirements are a vital component of all rewards in online casinos. You can't just get a bonus, and withdraw your money immediately.
You will need to play with your bonus money before being allowed to make a withdrawal.
Wagering criteria specify how many times you need to play for a withdrawal with your bonus money to "unlock" them. For instance, if you get a $10 bonus with 40x wagering requirements, it means that before making a withdrawal you need to place bets with a total value of $400.