You obtain eligibility for Social Security through the accumulation of retirement credits. When you pay FICA or self-employment taxes, you earn these credits. Even if you work part-time on a consistent basis, you will receive four credits each year, which is the maximum annual accrual.
Once you have 40 credits to your name, you will qualify for Social Security. If you have not earned enough retirement credits, but you are married and your spouse has done so, you can qualify based on the your spouse’s work record.