Most shower doors are made of glass. A glass door has hinges installed on the door jamb and door itself to keep it swinging freely. If the hinges are loose, or adjusted improperly, the bottom of the door may drag along the base of the shower. This can cause the door to crack or splinter at the bottom, or possibly break. Adjust the hinges as soon as you notice any interference in the door's movement.
Pry any plastic caps off of the hinge screws using a flathead screwdriver.
Remove all screws from the hinge side of the door and lift the door out. Set the door aside. Tighten any screws going into the door jamb.
Inspect the screws for damage and replace as necessary.
Hold the door with the screw holes of the door aligned with the hinges. Insert screws into the holes and tighten halfway. Have a helper place a spirit level on top of the door. Adjust the door until the bubble in the spirit level is even, then finish tightening screws.