It's all set out here - Social Security Online - The Official Website of the U.S. Social Security Administration

See your local office.

You can start here :

Social Security Online - The Official Website of the U.S. Social Security Administration

It's best to go there in person and bring along your identification and marriage license and your husband's death certificate. Also be sure to bring along his SSN as well if you know it. This will speed along things once you're there. You don't need an appointment either. Just show up in their office during regular business hours and wait for the next clerk to speak with you. The wait is not that long either.