Money you earn as a DoorDash delivery person is self-employment income. You are required to report even $400 of self-employment income and pay self-employment tax for Social Security and Medicare, and perhaps ordinary income tax, depending on your total amount of income.
https://ttlc.intuit.com/questions/2926899-how-does-my-side-job-affect-my-taxes
https://ttlc.intuit.com/community/self-employed/help/what-is-the-self-employment-tax/00/25922
https://ttlc.intuit.com/questions/2902389-why-am-i-paying-self-employment-tax
https://ttlc.intuit.com/questions/1901340-where-do-i-enter-schedule-c
https://ttlc.intuit.com/questions/3398950-what-self-employed-expenses-can-i-deduct
https://ttlc.intuit.com/questions/1901110-do-i-need-to-make-estimated-tax-payments-to-the-irs
https://turbotax.intuit.com/tax-tools/calculators/self-employed/
DOORDASH, INSTACART, GRUBHUB, ETC.
And you must report ALL your income, tips included. Tip income is taxable.
That's $400 of net income after expenses (income includes tips). In the case where you make more than $400 gross income, but your expenses offset the income, you may not be required to file. However, it may still be to your advantage to file to get the expenses on the record.
Also, if you file a tax return for any reason, then you must report all your income, even if your net-profit from a side gig is less than $400. The $400 threshold only applies if self-employment is your only income.