This connects hot and cold water, got that. It turns on the shower head, got that. If you don't have a tub, what is the 4th water connection for? Can it be for a hand held shower head ACROSS the shower on a different wall?
You would need to cap it off if not using it for a tub spout. You cant use it for a shower head and hand shower cause there is no way to divert it like a diverter tub spout would have.