Warning potential spoilers/ruining here, going to not go into specifics just give the different groups/motivations and plot line to the story:

There is an emperor and great houses (think Game of Thrones here), emperor directs the houses what to do, it is implied though that a house can take over emperorship if you best the emperor and his army. Arrakis (desert planet) is where spice is mined, spice is used for everything but particularly space travel. The freemen think indigenous tribe have lived here for a long-time. The Harkoneens (one of the great houses) mine the spice and kill freemen to keep them in check. Spice makes them extremely rich.

The emperor directs the Harkoneens to no longer mine spice and turns Arrakis over to Atreides, the Duke, his wife, and son are the main characters here. The emperor though double crosses Atreides, he gets the Harkoneens to attack Atreides on Arrakis and even sends some of his own elite army, Sardaukar to kill Atreides and his family, effectively destroying his house. The reason for this is the emperor felt the Atreides house was getting to powerful.

HokieForever