Autosomal DNA Matching: A Diagram

When you test your autosomal DNA, you reveal bits of your DNA from any one of your ancestors.  Your genetic distant cousins in the database are a match with you because you share the same identical little segment of the same ancestor.  The trick is to figure out which ancestor you both have in common.  The common ancestor could be along any of your lines and any of their lines and could be many generations ago.

People without extensively documented trees may have a problem making connections to their genetic distant cousins.  This should not hold you back from testing your DNA and may be the only way of discovering otherwise elusive lines.  DNA testing does not replace "traditional" genealogical research of original documents, census entries, cemetery records, etc.  DNA testing can also reveal ancestry for people who are adopted and, if a close match is in the database, can reveal the family of origin.