The Through-Ring will hook through the ring body and pull the bottom of the ring. It is typically left permanently hanging from the lead ring, and you'll use one wand per panel. Make sure to have plenty of space between the rod and ring.
The Over-Rod can be hooked through a ring or over the rod itself, and is more easily attached/detached than the Through-Ring. When hooked over the top of the rod it will push the lead ring. The Over-Rod hook can be used when you don't have enough space between rod and ring to hook through the ring, or when you plan to use the same wand with multiple drapery panels.