Social Security retirement benefit payments are not automatic; you must apply for them.
Current rules allow you to apply as many as three months before the month in which you want to begin receiving them, and it’s a good idea to apply in advance since the application process can take some time. You are generally not eligible for benefits covering any period before the month in which you apply or in which you become eligible for benefits (whichever is later). However, if you retire at age 65 or older, you can apply at any time after you turn 65 and receive back payments of up to six months of benefits before the month in which you applied.