Schedule C is the schedule on which you show your business expenses if you are self-employed. Do you have a 1099NEC? Did you work as an independent contractor?
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
Here is what a Schedule C looks like:
https://www.irs.gov/pub/irs-pdf/f1040sc.pdf