To be able to deduct gambling losses you need to be eligible to itemize your deductions on Schedule A instead of using the standard deduction.
You can only deduct gambling losses up to the amount that you won gambling. For example, if you won $500 and lost $1000, you would only be able to claim $500 in gambling losses. What this means is deducting your losses allows you to avoid paying tax on your winnings, but nothing more.
For more detailed information, see this article: https://turbotax.intuit.com/tax-tools/tax-tips/Taxes-101/Can-You-Claim-Gambling-Losses-on-Your-Taxes...
