Car windows, whether they are operated electrically or manually, are moved up and down via a regulator within the door panel. When this regulator is damaged or the window falls off of its track, the window will fall into the door panel. A number of things can be wrong with a fallen car window, so it should be repaired by a professional mechanic. In the meantime, however, the window can get a quick-fix before it is taken in for repairs.
Grab the window and push it up until it's closed completely.
Insert the flathead screwdriver between the window and the door panel on the left side of the window.
Pull back on the screwdriver to open a gap between the window and the door panel, being careful not to scratch the glass.
Insert one of the rubber doorstopper wedges between the glass and the door panel.
Repeat Steps 2 through 4 for the right side of the window. The rubber door stoppers will provide the necessary pressure to hold up the window until it can be repaired.