they are automatically uploaded to your AMCAS application. AMCAS transfers the information from your app to schools periodically though a FTP I believe. so you don't have to send them individually, as you did SAT scores.
You don't have to release them, if you chose to you'll just get emails from schools telling you to consider them. When you apply to schools using amcas they will get your scores whether you chose to release them the day of your mcat or not.