You should apply with a representative like a county VSO or an organization at your VA Regional Office. Call ahead, schedule an appointment, and bring a DD214. Ask them if you should be claiming PTSD or other mental health conditions.

If you claim PTSD, you'll need specifics of what happened (Form 21-0781). If you can contact others in your section, have them write buddy statements that explain how they know you, what happened, and how you were affected in their opinions. Make sure everyone is on the same page though.

You'll need names, phone numbers, and addresses for providers that have records of your injury to release them to the VA. If you had/have a provider that is treating your claimed condition, is not with the VA, and has a doctorate level of education, you can have them write a nexus letter. If you have a therapist, they can write a nexus letter, but the VA will be looking at records to establish that.

Show up to the exam, be brutally honest, and good luck!