It can be hard to keep up with Game of Thrones and its vast world of characters, countries, historical figures, competing religions, magical entities, and mystical substances. So you may be wondering exactly what does dragonglass do on Game of Thrones? It's actually got a few uses, one of which is extremely important to Jon Snow right now as he prepares to battle the White Walkers and the Night King.
Basically, dragonglass is a name for obsidian, which is a real substance created from volcanic lava. According to Forbes, "When this lava flows, its margins cool far more quickly than the hotter cores. When there aren’t many crystals floating around in these margins, these margins chill so rapidly that they form obsidian glass." In the world of the show, dragonglass, known in Valyrian as "frozen fire," has more than one use, not all of which were known to the Valyrians who first discovered the substance. They used it as ornamentation on their weapons, apparently without realizing that it was the only thing that could kill undead snow zombies, according to Sam's research in Episode 1 of Season 7. It's value as a weapon against the White Walkers is the main reason Jon Snow has instructed his people to begin mining it immediately.
Sam's research in the Citadel has also revealed that Dragonstone sits upon a mountain of dragonglass. If dragonglass is obsidian, that is, frozen lava, does that mean that Dragonstone is sitting on a volcano? Dragonstone is the ancestral home of the Targaryans, where Daenerys and her team of Westerosi All-Stars are plotting their next move. Considering the name of the place, some sort of volcanic activity there would make a lot of sense.
Aside from being pretty to look at and making excellent White Walker weapons, there could be other uses for dragonglass. Valyrians apparently used dragonglass to make their glass candles, and the premiere episode seemed to hint that the substance could have medicinal properties as well. Some fans noticed in the first episode that the book Sam was reading mentioned dragonglass as a cure for something when ingested. While many speculated that this could be a cure for grayscale, those who have seen Episode 2 now know that the cure for grayscale is way more disgusting and painful than ingesting glass.
While dragonglass has evidently been used for many things, in the coming episodes, I anticipate we're going to see it used for one thing in particular, and that is killing White Walkers.