Stick a heavy-duty suction cup near each of the two top corners of the glass panel.

To attach the suction cups, first position the suction cup with the movable handle parallel to the face of the glass panel (as indicated in the second picture).

While lightly holding the suction cup against the glass, raise the movable handle until it is parallel with the other handle (as indicated by the third picture).

If your suction cups refuse to stick, try cleaning both the glass panel and the suction cup with a damp soft, lint-free cloth. (Dampen with distilled water, and if needed, an equal ratio of distilled water and white vinegar for best results.)

Do not use the suction cups to carry the display glass because if one of them fails to stick, you could drop the screen and break it.

The original iMac box makes a good place to store the glass panel. Otherwise, a padded horizontal surface, like a towel on a desk, will do nicely.