The reasons people get their DNA tested for genealogy includes connecting with distant cousins or finding relatives, using what they know to fill in and expand the family tree, and break down brick walls. Testing yDNA takes you back 338,000 years, mDNA 200,000 years, and atDNA about 200-250 years which is equivalent to about 7 generations. If you are looking for family, the atDNA is of course the most important information.
Dr. Gleeson defines a “Match” as someone that shares an identical segment of DNA compared to you. It means that you have a common ancestor.
The Secrets to Success with DNA genealogy is 1) Start with the closest matches 2) Share your trees 3) Develop relationships with your matches, 4) Keep track of everything you have done with good notes.
After you get your matches and compare trees, position the people on your tree as close as possible. If the DNA site says that they are your 3rd cousin, you will share 2Xgreat grandparents so you are comparing your 8 couples of 2XGreat Grandparents with theirs. If you are adopted you are penciling in their 2xGreat Grandparents as yours. There are charts that help with the estimated positioning. The numbers can be thrown off my intermarriage within a family and groups like Jewish and Jehovah Witness that tend to intermarry within religion. You can look on Google, Wiki Tree, Ancestry, and other online trees for more information.
After positioning as many matches ancestors together you can start to eliminate the non-contenders. There are several tools that speed up all this research like GEDMatch.com. If you are adopted, go to DNAAdoption.com for very helpful information.