I throw it then hit buttons then it does damage?
In broad sense, yes. Enemies affected by bone dust brew have a 50% chance to be struck by your abilities a second time for 35% damage. It also has another effect based on your spec. For ww if SPK hits a target affected it refunds 1 chi. For BM tiger palm and keg smash reduce brew cooldowns by an additional 1 second. Don’t know about mw, don’t play it.
As a Brewmaster, I find usually 6-8% of my overall damage (raids) is directly due to my Bone Dust Brew. It has a 1 min CD but usually gets down to 40-45 seconds for Brewmaster after reductions.
For Mistweaver, if your target is coated in the brew like mentioned above they have the same 50% chance to get an additional 35% of your heal. They also get a little extra heal too just due to being coated. “Gust of Mists heals targets with your Bonedust Brew active.”
Obviously, only targets coated in the BDB will give you any kind of benefit - so be sure that you hit yourself with it too if you’re in the area. As a BM, I still get decent bit of healing from BDB just be making sure I get hit with it - usually 2% of my overall.