Whether you'll be required to actually pay taxes on your earnings (including tips and withdrawals, as well as any Challenge winnings) will depend on where you live, as well as other factors, such as your total income, and are your own responsibility.
Vocal operates under federal tax laws in the US, which means that at the end of each year, we're required to send out 1099 forms to any user of the site who's earned $600 or more on Vocal within that tax year—these forms are just a summary of your income that came from Vocal, and may be necessary for you to use if and when you file your own taxes for the year.
For this reason, we may ask you at any point to fill out a W-9 form (if you're a US resident) or a W-BEN form (if you're located outside of the US). These forms simply provide us with your basic taxpayer information so we're able to provide you with the summaries of your earnings when we're required to.