When you earn money working, your income is usually subject to social security and Medicare taxes. Usually, when you work for a company, you are their employee. As their employee, you only have to pay half of these taxes while your employer pays the other half.
If you received a 1099-MISC with the amount of the income in Box 7, Non-employee Compensation or a 1099-NEC with the amount in box 1 (starting with tax year 2020), you are considered an independent contractor rather than an employee. As such, a Schedule C must be filed in order to claim the income and calculate the correct Social Security and Medicare taxes based on your income.