Build a Family Tree Online - Look in the Social Security Administration Master

[Jane Tilly]

If you are an amateur genealogist, researching your family tree, you
already know that you start with yourself, and then your immediate
family.  You will want to use a blank family tree and pedigree
chart to record information about your immediate family members.
For each person, you record key information like full name, date and
place of birth, date and place of death, spouse, children, and
parents.  You also, of course, record, any other important
information that is compelling about your relative.
As you reach beyond your parents and grandparents, however, you will
need to use secondary documents and records to gather the information
you seek.
The usual places to look for data include birth records, marriage
records, divorce records, immigration records, military records,
criminal records, census records, and death records. 
Of course, you will also need to search for these records outside the
United States as you go further back with your family.
You might also find some branches of your family tree have been
maintained by other relatives, as you search in the genealogical
centers such as the one maintained by the Church of Jesus Christ or
ones you find on the internet through sites like RootsWeb.com,
Ancestry.com, WorldVitalRecords.com, and MyHeritage.com. 
One fruitful place to look for documents is the Social Security
Administration Master Death File (SSAMDF).  This is a database
maintained by the US Social Security Administration, which records all
deaths that are reported to the Social Security Administration. 
This database is also called the Social Security Death Index.
This database is not a complete set of all deaths in the United
States, but it is the largest single database of deaths.  While
the data goes back to 1937, most of the records are from 1962 onwards,
which is when the SSA computerized the process of keeping records.
The SSAMDF contains the following information:
-full legal name
-social security number
-date and place of death
-date and place of birth
-names of parents
-place of birth of parents
-cause of death
-burial place
Even if you know where and when someone died, this database can give
you more information, as for example, it gives you parental names and
places of birth, and it gives you a social security number (if it
existed).  Knowing the number, you can ask the SSA for the social
security application which can give you more information you may not
have had.
Unfortunately, this database is not available directly from the SSA,
but is made available to a large set of vendors who provide the
information to the public.  The sites mentioned above, all
provide searches of the SSAMDF.  They will all charge a
membership fee, but for most of them, the fee covers access to all of
their other databases as well.