Measure from the top lip of the tub or shower, up the wall on both sides of the tub or shower, to match the height of the shower doors. Mark this measurement on the wall with a pencil.
Take the brackets for the header of the sliding doors and place it against the wall at the marked location. Mark the location of the bracket's bolt mounting holes onto the wall.
Drill holes at the marked locations and insert mounting wall anchors. Use the anchors provided with the doors or those recommended by the manufacturer. Since the anchors support the track, which supports the doors themselves, it's important that they can support the weight.
Mount the brackets into the wall anchors with the provided hardware.
Snap the header assembly onto the wall brackets. Place the glass doors into the track. Stick the door jambs provided with the doors onto the walls at each side.