American Medical College Application Service
AMCAS is the application service for Medical School, and is part of the AAMC (American Association of Medical Colleges). AMCAS is the primary application (and is the common application you will send to all US Medical schools except those in Texas). You can begin learning more about the AMCAS application at any time on the AAMC website.
You will see in the Primary Application page that there are also Dartmouth specific details you will need to know when filling out your AMCAS application.