Don't sweat it :)
We live in times where it takes bachelor degree to operate most of every day stuff.
I read Mercedes forum a lot and my understanding is that >90% of owners have no idea they have hill descent and hill holding.
While hill descent is not crucial for a car, hill holding is very nice option, especially in California hills as you don't need to hold the brake when waiting for green light uphill.
What is stupid IMHO is that Mercedes makes the option available only on Comfort setting, that moves the car with 2nd gear.