The Door Dash income will increase your total income and you might owe more income tax which will reduce your refund. And you will owe self employment tax on it. You may want to increase your withholding at work to cover the extra tax on the Door Dash.
Self Employment tax (Scheduled SE) is automatically generated if a person has $400 or more of net profit from self-employment. You pay 15.3% SE tax on 92.35% of your Net Profit (If it is greater than $400). The 15.3% self employed SE Tax is to pay both the employer part and employee part of Social Security and Medicare (FICA). So you get social security credit for it when you retire.
The SE tax is already included in your tax due or reduced your refund. It is on the 1040 Schedule 2 line 4 which goes to 1040 line 23. The SE tax is in addition to your regular income tax on the net profit.
To report your self employment income you will fill out schedule C in your personal 1040 tax return and pay SE self employment Tax. You can fill out Schedule C and enter Self Employment Income into Online Deluxe but if you have any expenses you will have to upgrade to Premium version. Or buy any of the Desktop programs. All the Desktop programs have all the same forms, but you will get the most help in the Home & Business version.
How to enter income from Self Employment
https://ttlc.intuit.com/community/self-employed/help/how-do-i-report-income-from-self-employment/00/...
Where to enter business expenses
https://ttlc.intuit.com/community/entering-importing/help/where-do-i-enter-my-self-employment-busine...
