You have 23 chromosomes from each parent made up on DNA. One each has your Mitochondrial and if you are a male in addition has your Y DNA.

Y DNA goes from father to son only.

Mitochondrial DNA goes from mother to both sons and daughters but only the daughters pass it on to their children.

They are used in genealogy but only as a tool. For either to mean anything you have to have to be able to match yourself with another family tree and that requires research on the part of you and a person in the other family tree. It just doesn’t mean you can say we have a perfect match so we must be 2nd cousins. Also it doesn’t include all your ancestry. For instance your paternal grandmother and maternal grandfather will not be part of the resuts. If you get back to your 6xgreat grandparents, you are directly descended from 510 individuals. Of those 510 people you get your Mitochondrial DNA from only 8 and if you are a male, you also get your Y DNA from only 8 leaving out 494 people. However, if you use the test by matching yourself with other family trees and along with research, your will probably find some of the left out people.

Here is the best company for Y & Mitochondrial

http://www.familytreedna.com/

Now, some people just want to get an understanding of their regional/ethnic roots. Y & Mitochondrial are not good for that at all. One company that only uses Y & Mitochondrial advertises that they will help you "discover your deep ancestral roots." It is true for those two lines. They will assign you to a Haplogroup based on your DNA and show you the origin of your nomadic ancestor going back thousands of years. However, it is only in 2 lines and you come from a myriad of family lines.
The number of people you descend from pyramids as you go back.

There is a company that will match you with population groups throughout the world by using your Autosomal DNA. They are not going to tell you that you are 1/2 of something, 1/4 of something else and 1/4 of another something else. The same DNA crosses national, racial and ethnic boundaries.
They will give you your top 20 matches from their database of 849. The 849 matches in their data bases are from 100-150 samplings each.

The company that does this is

http://www.DNAtribes.com

Now I asked DNA tribes if my sister with whom I share both parents had the same Autosomal test and they advised:

"Two siblings will each obtain unique results. Family members do typically share some regional or ethnic genetic affiliations, but in some cases matches can vary substantially between siblings."

You get your Autosoma DNA 50-50 from both parents but when you get back to your grandparents it is not necesarily at 25-25-25-25
breakdown. You get 50% from your maternal grandparents and 50% from your paternal grandparents, but the breakdown in both cases between grandmother and grandfather is not an even split and it can vary between you and all your brothers and sisters in different ways.

FamilyTreeDNA does do Autosomal testing but they would not give me an analysis. I had to send my results to DNATribes.

Someone asked me if I know the results were accurate and I said I don’t know how you could determine this. Since within any nationality, race or ethnicity there is no absolute purity. If you had 2 companies that both did the tests I can see how results would vary as one company might not have samples of certain groups that the other company might have.

There is another company that does Genealogy DNA for free, but they won’t send you a report.
They will put the results on their website but no analysis. It took about 6 months for mine. However, you could set up a temporary account with Ancestry.Com and feed your results into their website. They accept results from other companies.
The company that does the tests

http://www.smgf.org/pages/how_it_works.jspx

Here is another link that might help you in understanding DNA.

http://www.pa.msu.edu/~sciencet/ask_st/060293.html