It's a harder coating that essentially acts like a repellent to dust, bugs, and other gross stuff. Most coatings also are very hydrophobic, so water beads off them very easily (which also tends to be why dust comes off easily). Basically, think of it like a semi-permanent wax on your car.
For a professional coating, it usually ends up being $3-5k, and they are supposed to last ~5 years.
Things it WON'T protect from: door dings, rock chips, or scratching.
Honestly, I don't think they're worthwhile. It's a lot of money, and you still get rock chips all the same. Sure, your car tends to look a lot nicer, but so does waxing your car every once in awhile.
I've noticed a trend regarding everyone talking about them: This same thing happens whenever a brand new car is released ANYWHERE. Super enthusiast folks show up and want to make sure their car looks super shiny all the time, so they pay for these coatings and talk about them and document them extensively. Same thing with the protective film people.
I can tell you I saw the same threads showing up on the Subaru BRZ/Scion FRS fan forums right after release of the car back in 2013. This was a 25k car, and people were getting ~3k coating on that car too. Not too many of those threads these days over there...