The Baron is hugely fat, living a corpulent, decadent, and perverse life. He wears a suit of anti-gravity suspensors so he can move around, be comfortable, and not die under his own gigantic weight.
The Baron is the head of House Harkonnen, one of the many noble Houses that sit in the Landsraad, the defacto government of the galaxy. They are governed over by an Emperor, Shaddam Corrino IV, from the House Corrino. This creates a balance of power, along with other interests such as the Bene Gesserit, CHOAM (the business arm of galactic rule), and the Spacing League (the intergalactic travel and commerce faction). All the various factions work together to keep money and power, but they also jockey against each other for advantage. House Harkonnen and House Atredies hate each other due to a long, generational vendetta between their families.
The Bene Gesserit voice is one of their many "witch" powers. They have very fine, nearly total control over their bodies, and are trained to use the pitch and tone of their voices to reach beyond the conscious mind, and deep into the subconscious where their commands bypass normal human thinking and are obeyed without question or even being thought about. Any individual not trained to resist such mental and physiological control simply does what they are told to do by a trained Bene Gesserit wielding the voice power.
As for Star Wars comparisons, Dune was one of the first, and you can find it's influence over so many things. In the same way that JRR Tolkein affected (and created) so many fantasy staples with Lord Of The Rings, Frank Herbert did the same for science fiction with Dune.
I would certainly recommend the first three books. This is the story of Paul Atredies, and the start of his son's story (Leto II). The fourth book I'd also recommend (end of Leto II's story) as this finishes that story started in the first three books, but it's quite distinct, in a very different setting, and far in the future. The books after that get progressively more bonkers, and I think most people see diminishing returns after that point. The further books written by Brian Herbert after the death of his father are not very good in comparison to Frank Herbert's seminal first three/four books.