Start with yourself & work back.
If you have your birth certificate, it will have your parent's names on it.
If you are younger than 40...you may then have to look for their birth
information (your birth certificate should give that info & their age at the
time of your birth).
Actually, I can follow my grandson's (he's 19) back from his birth to Ellis
Campbell b 1804 ...which is where our Ellis drops in from outer space.
Once you have your parent's info, you can look for their parent's.
A good place to start (free) is http://www.familysearch.org
The information there will mostly be from family info submissions...so will
need to be verified, but it's a start.
I have Ancestry all inclusive (World) and if you want I can do some checking