"where I would attach the door to"

If the existing jamb has a place for a storm/screen it should be readily apparent.

If there is not a place for it things get a little harder with a wood door.

You may need to add some trim around the opening to create the jamb needed for the wood storm/screen, or surface mount it onto the jamb and add a stop bead.

Metal storm doors often come with a frame that can be surface mounted on the existing jamb.