Independent contractors make their Social Security payments via the SE (Self-employment) tax. See this IRS reference for a detailed explanation:
https://www.irs.gov/businesses/small-businesses-self-employed/self-employment-tax-social-security-an...
Independent contractors may have to make quarterly estimated tax payments, because taxes are not withheld from payments made to them. Those estimated tax payments can be used to pay the self-employment tax.
The Self-employment tax is reported on Schedule SE, which is attached to your 1040 personal tax return.
https://www.irs.gov/pub/irs-pdf/f1040sse.pdf
**Answers are correct to the best of my ability but do not constitute tax or legal advice.
