As a food delivery person, you are considered an independent contractor, meaning Postmates doesn’t withhold any taxes.
If you make more than $600/year with Postmates, they will send you a 1099-MISC form with your annual earnings. You should still report your earnings to the IRS even if you don’t make $600 with Postmates.
You can write off the mileage on your car, but you’ll need to be tracking that throughout the year. Postmates recommends using the Everlance app to track this.
Learn more about tax time at How to Handle Taxes for Your Side Hustle.