If you're not all that familiar with the theory of evolution and want to better familiarize yourself with the evidence establishing the theory (as well as the fact) then you will want to consult Jerry Coyne's Why Evolution is True.
Extremely lucid and accessible, the book introduces the reader to the basic lines of evidence demonstrating the book's title. Given how controversial evolution remains in the US, despite it being one of the most robust theories in science, this book may be worth your perusal.
For more on the book:
- Coyne at Point of Inquiry
- SciAm's podcast discussion with Coyne
Coyne also has a blog titled Why Evolution is True.