You are a business in the IRS's eyes.
You do not have to carry on regular full-time business activities to be considered self-employed. You will file this income on Schedule C.
To file a Schedule C, here are the steps:
- Sign in to your account and select Pick up where you left off
- At the right upper corner, in the search box, type in schedule C and Enter
- Select Jump to schedule C
- Follow prompts, you might be prompted to an upgrade if you have expenses