The exhaust brake on my 2017 has two modes. One is the full exhaust brake. It lights a yellow light on the dash. It works best in tow haul and activates when you apply the brakes. The other (second push on the exhaust brake button) lights a green light on the dash. It is the automatic brake but I know less about it cause I don't use it.
In FULL mode the exhaust brake will engage any time when decelerating AND the rpm's are above 1200 AND the TC is locked. In AUTO mode the same rpm and TC requirements apply however it won't engage until the brake pedal is depressed (I've found just enough pedal to activate the brake lights to be sufficient) this allows coasting. Using tow/haul while in AUTO will bring in automatic downshifting while braking also.
If you need manuals you can go to ramtrucks.com and select the "owners" tab where you'll be able to DL them. You can also register on the site, enter your vin and find more information on your vehicle.
Sometimes I am thankful for the older models. 2012 has an on/off for the exhaust brake. Pretty simple
Start the truck, turn it on and don't think about it any more. A slight pressure on the fuel pedal keeps if from engaging if I want to "coast".