The National Center for PTSD (NCPTSD) is provided by the U.S. Department of Veterans Affairs. Its aim is to advance the clinical care and social welfare of U.S. Veterans through research, education and training on PTSD and stress-related disorders. The site is an educational resource on PTSD and traumatic stress, for veterans and also for mental health care providers, researchers and the general public.
The PTSD Information Center has Fact Sheets and Videos to answer your questions on trauma, PTSD and related issues. A good place to start is What is PTSD?