Arrakis is notable for containing reserves of the highly-valuable substance the "spice melange," which increases awareness and extends the physical life of those who consume it. When taken by individuals with latent powers, the spice can also lead to vivid prophecies and greater perception.
Spice is used by several powerful groups in the Imperium, including the Guild Navigators, who employ spice's mind-altering abilities to travel through space and time. Long term exposure to spice can cause the eyes to turn a bright blue.
Even though there is a large population of indigenous people, called the Fremen, on Arrakis, Houses in the Imperium are frequently appointed as stewards of the planet, and given responsibility for the lucrative task of mining and shipping out spice all over the empire.
Since spice mining yields so much profit and power, to be chosen as steward of Arrakis is, in theory, a great honor.
But the planet is hostile in more ways than one. The scorching heat and frequent sandstorms are a hindrance to spice production, as are the horrifying sandworms, which are drawn to rhythmic noises such as those emitted by spice mining operations.
The Fremen can successfully navigate Arrakis's harsh conditions — they wear protective clothing called stillsuits, which help keep the user cool and recycle moisture emitted from the body into drinkable water.
They've also devised ways of moving that avoid attracting the worms, the largest of whom is considered a god by the Fremen and referred to as Shai-Hulud.
Fremen culture is rich and complex, and also includes a prophecy of a messiah, called the "Mahdi," that's heavily influenced by Bene Gesserit doctrine. When Paul arrives on Arrakis, he's referred to by some as the "Lisan al-Ghaib," or the "outsider prophet." Some even begin to suspect that he's the Mahdi.
In "Dune," the leader of the Fremen tribe at Sietch Tabr ("sietch" being the Fremen word for village, and Tabr the location on Arrakis) is Stilgar (Javier Bardem), who forms an uneasy alliance with the newcomers to Arrakis.
Chani (Zendaya), a Fremen woman who captures the attention of Paul, is also part of the Fremen at Sietch Tabr.