go to this link, click on BT Gold, and you can read about it. They basically fire by rotating the release, there is no trigger. The whole concept is based on using your back muscles to hold and fire the release while focusing on your target.
I could write about it for days, but this link will help you get started.
http://www.truball.com/Instructions.html
zenitharchery.com also has a decent reading about it.