I am a college student doing DoorDash, I have no expenses, how do I mark this?

Anyone who operates a business as a sole proprietor must fill out Schedule C when filing their annual tax return. Schedule C accompanies the main tax return form, 1040, for taxpayers who must report a profit or loss from their business.  You do not have to enter any expenses. 

If you have any income associated with DoorDash there are a lot of expense you may be able to claim.  This would directly offset your income and lower any Tax you may owe. 

Here are some common expenses you may be able to deduct:

• Mileage. It's essential to keep track of all of the miles you drove for business. 
• Parking and tolls. 
• Mobile phone. 
• Supplies. 
• Roadside assistance. 
• Commissions and fees. 
• Bike and accessories.

for more information follow this link-

Schedule C: Who needs to file and how to do it