Use the tape measure to measure the inside width of the windows along the arched top edge between the two points where you wish to install the curtains on the arched windows. Write this measurement down.
Purchase a flexible curtain rod for each arched French door window using the measurement data you gathered. Cut the curtain rods with tin snips so they will fit the inside top edge of the windows.
Install the mounting clips inside each window frame at the upper left and right corners using the mounting hardware included in the kit.
Measure the height of the window from the highest point of the curved top edge to the bottom of the window. Purchase curtains designed for arched windows that will fit the height of the French door windows.
Slide the curtains onto the flexible curtain rods. Place the curtain rods onto the mounting clips and adjust the curtains so they cover the windows evenly.