Step 6: Window Hooks
The hooks will go on the loops of string, and over your window frame, or over the opening arm, or a handle - whatever you've got. Mine are happy to fit over the frame, and the hooks are thin enough that the window still closes with them in place, no problem.
You'll need to take a look at your own windows to see exactly what size of hook you need to make from the two paper clips.
Follow the images to see how I fold a hook with a loop on the end for the string to pass through. Don't forget you'll need two.
The paper clips don't have to be as flashy as mine - ordinary ones work just as well, if you're less stylish than I am.