Your starting point should be the following web-site:
The starting website of AMCAS (American Medical College Application Service) can be found here. AMCAS is a centralised application agency where you send in a very comprehensive application, including all extracurricular activities, transcripts, MCAT results, academic achievements, and a short auto-biography. You also send in large amounts of money, and a list of US schools that you want this application forwarded to.
AMCAS then distributes this application to the US medical schools, at which time they will send back a secondary application, often requesting additional money and perhaps some supplemental information, such as essays or reference letters. Past that, you must wait for interviews, and then an acceptance letter.
I applied to some American schools, but only got as far as the secondary application. At that time, I decided I didn't want to go any further into the process, and stopped. As a result, I don't know if there are any other steps that need to be obtained. eg. student Visa status, etc.