First, separate the mirror from the hanger tab ( white metalic piece in your pic ). A special adhesive ( available in any auto parts store ) must be used to glue the metalic tab to the windsheild first Then hang/attach the mirror. Tip: make doubly sure you have the tab right side up and in previous location prior to attaching it to windshield. If you made a mistake and need to remove the tab from WS, use a piece of wood ( 2x4 works good ), place it against side of tab and give it a healthy whack to dislodge.