If you were told there was a book on your family history with specific information not available anywhere else would you want to read it?
The DNA in each of trillions of cells in your body is a copy of that book. It's huge, something like 3.2 billion letters. Although much is not genealogically informative the part that is constitutes a text equivalent in length to the Gospels of Matthew, Mark, Luke, and John combined.
A decade ago if someone suggested you start your family history research with DNA they'd be considered crazy. Today it may be the best starting point for some, especially adoptees without access to biological parent information. For the rest of us, we can still expected to find information from DNA not available from traditional genealogical sources.
A good source for information is the Frequently Asked Questions at Family Tree DNA. It's part of the learning centre resources at the FTDNA site, although some of that content is a bit dated.
Right up to date, to the extent that the last segment isn't even published, is a four part series DNA Testing for Genealogy – Getting Started by CeCe Moore (Your Genetic Genealogist) for Geni.com. Read parts one, two and three.