Just doesn't list what was withheld or nothing was actually taken out? If no deductions are being taken out, you are not an employee, you are an independent contractor. GrubHub will issue a form 1099-Misc, after the end of the year, for you to report your taxes. In addition to income tax, you will have to pay both the employer and employee shares of social security and medicare tax.
For more info, see https://turbotax.intuit.com/tax-tools/tax-tips/Self-Employment-Taxes/Filing-Taxes-for-On-Demand-Food...