Just bought a Dodge Ram 2500 Diesel 6.7 and I'm confused

Use of the ebrake saves on wheel brake (truck and trailer) wear and tear. I use it 100% of the time. For city driving it barely turns itself on, but for highway use its great.

The tow haul helps the truck select the right gear for hauling.

The +/- buttons limit the highest gear your truck will use when descending hills. Its not uncommon for me to 'coast' all the way down a long hill without touching the brake or gas as the truck does all the work.