Beyond the well-charted territories of Arrakis, beyond its infamous sandworms and treacherous sandstorms, there exists a realm more desolate, more enigmatic – Zerakis.
These hooks allow the Fremen to mount and steer the giant sandworms, and even though Paul is told not to show off during his first ride attempt, he's clearly quite good at it.
Fremen are able to use Maker Hooks to steer a sandworm by hooking into gaps in the sandworm's plating, forcing the creatures to instinctively move in the opposite direction.
It's likely that this scene is part of a " spice agony" — a ritual in which members of the Bene Gesserit voluntarily ingest a poison known as the Water of Life — liquid harvested from sandworms that die from drowning.
Out of the sand haze came an orderly mass of flashing shapes—great rising curves with crystal spokes that resolved into the gaping mouths of sandworms, a massed wall of them, each with troops of Fremen riding to the attack.