Fill with water and hook onto the belt/pants.
The wetstone holder has a hook on the back that you fasten around the belt/waistband.
The best option is to have a sturdy leather belt, you don't need to have it inside the pants but just outside the shirt. Poor alternatives are attaching the holders to pants pockets or loosely fitting clothes. They should sit tightly against the body without flapping during your movements.
You always have the wetstones with you, and you fill the holder with water so it's half-full with the wetstone. Those of us who work a lot with the scythe or professionally always carry two wetstones with us in separate holders.
Whether the holders hang on the right or left hip is a matter of preference, most people choose the right side.
Occasionally, you may need to remove some grass that gets stuck at the bottom and starts to smell bad.