No self respecting road user would drive with cracked brake cables or flat tyres. Likewise, no motorist with any sense of self preservation will attempt to drive with a cracked windscreen. Not only is it illegal to drive with a cracked or broken windscreen, it places the driver and other road users in danger, as it obscures the driver’s vision and allows moisture to permeate the car and fog up the windows.
Unlike tasks like changing a timing belt or catalytic converter, changing a windshield is not too difficult a task for the motorist to attempt themselves, if the motorist is careful to follow a few sequential steps.
Purchase correct windshield for the car from an authorised stockist. If the new windshield is being transported by vehicle, ensure the item is protected with cushions and blankets to avoid damage in transit. Before installation, detach protruding items that are in proximity to the windshield like rear view mirrors and wipers. Then, wearing protective gloves, check the rubber gasket around the window for damage. If it is cracked or damaged, a replacement is needed. If the rubber gasket is undamaged, carefully remove it using a screwdriver and knife. (See http://www.wikihow.com/Replace-Your-Automobile-Windshield)
Gently push the cracked or broken glass away the frame by pushing from the inside. Take care to ensure the heavy windshield glass does not shatter during removal. If necessary seek the assistance of another adult in this task. Ensure the exposed frame is free from dust and dirt prior to insertion of the new glass. (See http://auto.howstuffworks.com/under-the-hood/vehicle-maintenance/how-to-replace-windshield.htm)
Carefully place the rubber gasket around the replacement windshield. Place the inside of the gasket into the inside of the glass, using an appropriate sealant on the outer edge of the gasket while lowering the glass into the frame. Finally carefully press the new windshield into the frame and wipe any residue of adhesive with a dry cloth, and drive away carefully!