You'll have to start with getting all the information you can on the persons you know, then asking anyone else who would have information (i.e. neighbor, family friends). Take the information you've gathered and start searching for records. Birth Certificates, Marriage Licenses, Death Certificates, Divorces Records, Social Security Death Indexes, Obituaries, Cemetary Records, etc. There are many places and tools to do searches. (i.e. Google, Family Search, Find a grave, newspaper archives, WikiTree, Ancestry.com, Libraries, military records, etc.)
Start with Yourself, then your parents, then Grand Parents and so on.This investigation will likely generate information you can use to get farther along with your ancestry.
My personal advise would be to Verify, Verify, and yes, Verify some more as you go.
Also as your searching remember that female surnames tend to change with life events like marriage and male surnames generally do not change. Also the farther back you go Surnames in general tend to be spelled in variations (i.e. by phonics) meaning spelled the way they sound instead of the proper spelling. So verifying with other identifier would be necessary.
Hope this helps.