For those who haven't read the book ...
The KWISATZ SHADERAC -- is a mythical savior, a Jesus-like figure prophesied to come and save the lowly FREMEN, the native people of DUNE, who for centuries have lived under the heel of a line of off-world freebooters; the Fremen are yoked to mine the only precious item on ARRAKIS, a place with virtually no water, which is why the desolate, mostly desert planet is also called DUNE. This "ore" is called the SPICE. The Spice is key to intergalactic travel, as it it used by the Guild navigators, big whale-looking brains that allow people to "fold space" and travel across millions of miles by teleportation. But the mining of this Spice is terrible, dangerous labor, there are constant threats from giant worms -- the irony is the waste matter of the worms is the raw material of the Spice.
The Kwisatch Shaderac will come one day to figure this out, saddle and ride the worm, use them the way Hannibal used elephants, lead a rebellion of Fremen and throw off the yoke of the rulers of current Arrakis, the Harkonnens. They are a bad sort, led by General Vladimir Harkonnen, a ruler, lech and ne'er-do-well. His Lefttenant is an assasin called Feyd Rautha.
A boy comes to Arrakis from his home world, a world like earth, a watery world led by a family called the ATREIDES. DUKE LETO ATREIDES is Paul's father, and the LADY JESSICA, a concubine, is Paul's mother. Lady Jessica is also secretly a member of the Bene Jessurit sisterhood ... well, anyway, Paul Atreides' father is betrayed and killed, and the Harkonnen wrest Dune from the House Atreides, but Paul Atreides escapes death with his mother, lives underground with the Fremen. There he is called Paul Muad'Dib; slowly he builds and leads a revolt by the Fremen, by using the amplified power of their own voices against the evil Harkonnen. He drinks the WATER OF LIFE, and does not die, which on a Bene Jessurit sister can do; it was written that the Kwisatz Shaderac would be able to do this.
Following Muad'Dib, the Fremen defeat the Harkonnen, and Paul is revealed to be the Kwisatz Shaderac. Other peoples come to Dune to pay homage, using the GUILD NAVIGATORS, who use the Spice as a sort of a drug that helps them FOLD SPACE, thereby making intergalactic travel not only doable, but quick and easy ...