Generally, Social Security Benefits are exempt from garnishment. The exceptions to this rule are debts to the U.S. Treasury and child support or alimony. If your creditor is owed any other debt, they usually don't attempt to garnish your Social Security benefits, as they know these benefits are exempt. But the creditor can garnish your bank account where you deposited your Social Security benefits, if those benefits have been commingled with other monies.
If you have "mixed" your Social Security benefits in a bank account with other money, you will need to claim an exemption against the garnishment action. If you have been served with a garnishment action, you must claim your benefits are exempt in an answer to the summons, and the judge must rule on what part of your bank account contains Social Security benefits, and is therefore exempt.
The exemption you should claim is under the authority of a particular Social Security Ruling (SSR 79-4), which says Social Security benefits are generally exempt from execution, levy, attachment, garnishment, or other legal process, or from the operation of any bankruptcy or insolvency law.
However, if you have any other assets or money (besides Social Security benefits) that you need to protect against creditors, you should consult a bankruptcy attorney or debtors' rights attorney.