How do you shift a 10 speed auto shift transmission?

My truck has a Fuller UltraShift automatic-shift transmission. I decide whether I want to go forward or backward. I step on the brake pedal and press the button that corresponds to the way I want to go, and the transmission shifts itself.

There's a button on the shift console for "manual" and if pressed, you use up and down keys to shift. If you do this, it's just like shifting a fully manual transmission except you don't have to shift the rear end yourself and there's no clutch. My truck has had six drivers including myself and none of us have ever pushed the manual button.