Clean the end of the copper pipe with a piece of emory cloth (cloth sandpaper) to remove any dirt or debris.
Place the compression nut onto the copper pipe so the open, threaded end faces the end of the pipe. Then slide the compression ring onto the end of the pipe.
Place the threaded end of the valve fitting over the end of the copper pipe. Slide the compression ring and the compression nut toward the compression fitting and thread the nut onto the fitting until the nut is hand-tight.
Place one crescent wrench over the compression nut and another crescent wrench over the compression fitting. Tighten the nut onto the fitting. Doing so will smash the compression ring onto the copper pipe to create a tight seal between the pipe and the fitting.