Rigging turns square sails without rotating the mast

How could square sails face different directions without rotating the mast?

Crews hauled on the running rigging to swing the yards and trim the sails to the wind while the mast stayed fixed.

A square-rigged ship's mast remains fixed while the spars supporting its sails can move. Crews haul on ropes to turn those spars and change the sails' angle. This allows the sails to face different directions as the rig is adjusted to the wind.