One of the newest trends in genealogy is the use of DNA to identify one's roots. This does not mean you don't have to still trace out your own genealogy.
DNA test can determine things in two different ways. If you participate in a surname specific DNA test is may allow you to identify a person was back. The large size of these samplings from several persons helps build a strong case to one person back in time. You still need to figure out how you are related to the person.
The other form of DNA testing helps you in identifying national or regional origins. It does not identify a specific person or produce a lineage. Interesting component to this test is that you often find out you are not made up of what you thought you were.
It is fun to do and see the results, but it does not stop you from doing a great deal of work. Enjoy.