Bonus wagering requirements tell you the number of times you must play through the bonus to turn it into fiat currency you can cash out.
Wagering requirements are always displayed as multipliers, for example, 30x. The multiplier tells you that you must wager an amount equivalent to 30 times your bonus to convert your bonus to real money.
When you go for a $500 casino bonus, you must always wager a fairly large amount.
This is because even if you claim a bonus with a relatively low wagering requirement, such as 10x, you still have to wager $5,000 to withdraw the winnings ($500 bonus x 10 = $5,000).
Hence, you should pick $500 casino bonuses with the lowest wagering requirements you can find.