Social Security is not just for senior citizens, but they probably are the ones most likely to need it often. The homepage is filled with information on Medicare, disability and retirement benefits, and office locations.
Anyone needing a new Social Security card can look here to find out to get one. Supplemental Security Income (SSI) is here. If you need a form or you want to check on your earnings, that's all here. Survivors of persons eligible for benefits can figure out what to do here. If you're self-employed, there's a section for you on the "Group" drop-down menu. Basically, if you're reading this blog post, go to this website and look around. It's packed full of useful, easy to find information, and even if you don't need it now, you will at some point - guaranteed.
The site is also available in Spanish and several other languages. See the links in the top right corner of the screen.