Interesting...I picked mine up at a model train store, but this might be the same thing. It’s literally a very fine powder. You can apply it with a dry brush. Just scoop some where you’d like it with the brush, then use the brush to rub it into the model where you want to see the effect. Use a tad more than you think you need, a lot falls off in the process (so do it over something like a box top so you can collect and re-use it) but what sticks really stays on well.
You get a really nice mat effect. I use it a lot for 40k vehicles and weapons (black and rust colored powders show nicely o