There are several companies that offer DNA genealogical tests. The first thing you should do is research the company. Make sure the company has a good reputation. Each company relies on its own proprietary database of DNA information. The larger the database is, the more accurate your results will be. And a respected company is more likely to stick around long after you take your test. Some companies will even send you updated information about your results as they refine their databases.
The tests themselves are simple and painless. Most involve using a type of swab. You use the swab to collect cells from the inside of your cheek. Just rub the swab against your inner cheek for about half a minute and you've collected enough of a sample to get a bead on your genetic background.
Tests can be expensive, ranging from around $99 up to several hundred dollars depending on the type of test. Before you order a test, you should be aware of what the results will mean to you. A DNA test can help you fill in gaps in your family tree or determine if someone with the same surname is directly related to you. But DNA tests won't give you the information you need to fill out your entire family tree. It's a useful tool but not the only one you'll be using to research your genealogical background.
If you're male and want to research your paternal line, you'll need to order a Y-DNA test from a reputable company. If you're female but want to know more about your paternal line, you'll need to have a male relative perform the test for you. If you're more interested in the maternal line, you'll need to order an mtDNA test. Both males and females can perform such a test on themselves.
Some companies offer different versions of the Y-DNA and mtDNA tests. Usually this means that one test uses more genetic markers than the other, giving you a more accurate glimpse at your family background. If you're trying to find out more about your particular surname, you'll need to order a test that looks at more markers than a general ancestry test. You may find some companies offering package deals in which you can order both a Y-DNA and mtDNA test. Other DNA tests can tell you if you're related to a specific person -- both people need to take the test.
Getting a test is as simple as ordering the right test kit from the company you have chosen. The company will ship the test to you. Once you take the test, you send the sample to the company for analysis.