How much information can you get this way?

I am just starting out researching my genealogy, and I am trying to do as much as I can for free since I don’t have a lot of money and I am just looking for a new interesting hobby. I have been told that some websites let you search the social security death index for free. How much information can you get this way? What do the results tell you? And what is the next step after this search? Can anyone recommend any other good free ways to find out more about your genealogy and family tree? I am really interested in learning more about my history.