If you know anything about Dune, you probably know that the hottest commodity in the Duneverse is a psychoactive substance known as the "spice melange" — or, simply, "spice." Aside from lighting its users up with radical blue eyes, the spice expands the minds of its users in miraculous ways and facilitates interstellar travel. Since its near-magical effects can't be artificially reproduced, it's become the backbone of the entire galactic economy. Whoever controls the spice controls the galaxy, and the spice is only found on one world: the hostile desert planet of Arrakis.
Why can't the spice simply be domesticated and cultivated on other worlds, you ask? Excellent question. Melange is not a plant product like most mundane spices, but rather a biological byproduct of the sandworm's life cycle. Over their epochal lifespan, the sandworms of Arrakis grow from tiny "sandtrout" to the massive Old Men of the Desert like the one you see in the last frames of Villeneuve's first trailer. As they molt and expand, they excrete large caches of melange beneath the desert sands. These spice bulges eventually "burst" up to the surface, a process that signals Fremen prospectors to begin mining.
Given the importance of the spice, you might wonder why no one's attempted to transport a sandworm off of Arrakis. They have, but the worms are so hydrophobic that they die almost immediately after being lifted from the desert. Dune is the only planet that can sustain sandworm life, and so Dune remains the center of power in the galaxy.
The inciting incident for the story of Dune is a transition of power on Arrakis from House Harkonnen of Giedi Prime (the bad guys) to House Atreides of Caladan (the good guys). As Duke Leto Atreides (Oscar Issac) and his son Paul ascend to power on Arrakis, they take control of the planetary spice mining operation — a seriously plum job. If not for the sandworms of Arrakis, there would be no spice, and thus no conflict. The sandworms are at the center of it all.
