The direction you are going is asking for serious trouble.
You are trying to install the valve in a manner and in a place where it shouldn't be installed. It is designed to be installed in a place where you have access to the back side.
The large straight threads are for a clamping nut to hold the valve in place. You may be able to make a connection at the end by using one of the flexible connectors that are often used as a toilet supply. That kind of supply should not be use in an inaccessible space.
You might find a supply hose in a "big box" store. If unsuccessful there, try a plumbing supply house. But if you hide that kind of connection behind tile it will not conform to any codes and you are risking grief when one fails.