What it administers. The core is the old-age, survivors and disability program, meaning retirement benefits, benefits for spouses, children and survivors, and Social Security Disability Insurance. It also runs Supplemental Security Income, the means-tested program for people who are aged, blind or disabled with limited income and resources, which is paid from general revenue rather than payroll taxes.
Numbers and records. SSA assigns Social Security numbers, and its regulations explain why: "The Social Security Administration (SSA) maintains a record of the earnings reported for each individual assigned a social security number." That earnings record is what retirement, disability and survivors benefits are calculated from, which is why the Social Security Statement is worth checking for missing years.
Its Medicare role. The Centers for Medicare & Medicaid Services runs Medicare, but Medicare.gov tells people who need to enroll to "contact Social Security," and online sign-up happens "at Social Security." SSA also determines the income-related monthly adjustment amount that higher-income beneficiaries pay on top of Part B and Part D premiums.
How independence came about. Public Law 103-296, enacted August 15, 1994, rewrote the governing section to make SSA an independent agency, and the change took effect March 31, 1995, separating it from the Department of Health and Human Services.
Disagreeing with a decision. SSA's regulations set out an administrative review process taken in order: an initial determination, reconsideration, a hearing before an administrative law judge, review by the Appeals Council, and then a lawsuit in federal district court. Each step usually has to be requested within a set period.
Its rulebook is public. The Program Operations Manual System (POMS) is, in SSA's words, "a primary source of information used by Social Security employees to process claims for Social Security benefits," and its public version is posted online, which makes it the place to read how the agency applies a rule.