I teach genealogy classes, and warn students that just as with anything found in research, be prepared to be shocked or disgusted with what you find.
There are several companies doing dna testing, and the more reputable ones (i.e FTdna) can provide basically three important things.
1. ynda mapping which basically allows you to link with other relatives to a common male ancestor.
2. mdna (mitochrondrial) Which does similar the same on the female line.
3. And most important to many, your haplogroup which provides the general location of your line. Like in my case, I am R1b1c1, which basically with general certainty is a celtic line that lived in western Europe, and most likely in the British isles, and very common in Scottish and Irish people. (no big shock there). Once you know your Haplogroup, you can check the migration maps for details.
Holy crap! You sure know some stuff!
He was hoping to get #3 but got #1 instead. He doesn’t need to find anymore worthless cousins.