I'm not sure about the 750, but on my CM 400 A Hondamatic, there is a button on top of the left rear brake handle. You push down on the button, pull the handle all the way back, and let go of the button. If it is working correctly, your bike will not move, it is like an emergency brake on a car.
To release it, pull the handle back and push the button, then let go of the handle.