For replacing the glass, it has to be figured first how it will be taken out. Even though it is shattered into countless pieces, the glass would have to be removed from the edges before installing a new one. For a door glass, the door panel has to be removed to access the mechanism that moves the window up and down. The glass is attached below. The fix auto glass and rear window glass requires the trim and the rubber gasket to be removed. The rubber gasket has to be replaced with a new one as the new one is installed. The car manual will be of help for removing and replacing the glass.
Automobiles are made so that a cracked windshield can be replaced; they are not made to be repaired. To my knowledge, manufacturers do not recommend or promote repairing windshields they recommend replacing them. A windshield is a structural part of the body and is in place for safety reasons. You shouldn't mess with the overall safety of the car by repairing a glass that is vital to safety during a rollover or accident.
As a windshield installer for the past thirty five years, let me give you three good reasons not to repair your windshield. As windshield repair is a gimmick in my opinion.
If you are using a system fix auto glass repair disc, boot the PC with that. Otherwise, after your PC has finished its BIOS sequence, hold down the F8 key. Choose Repair Your Computer from the Advanced Boot Options screen (below) and tap Enter.
One more thing to consider is the amount of things we can see through the windshield. If there is a difficulty in the driver's vision then it is common sense that there will be a higher risk of accident. Windshield plays a vital role in ensuring the driver's clear vision of the road. With that being said it answered the question why is it important to repair the windshield. It is very easy to find someone who can repair the windshield. All of whom are very competitive and knowledgeable so you don't have to worry.
The primary issue, whenever you want to mend a chipped windscreen, is whether you should repair or replace the glass. The majority of auto glass stores will try to mend a chip or crack, provided it isn't positioned right in the driver's line of vision. They utilize a clear resin which gets dropped on top of the chip and mended with ultra violet lighting. Then, the clear resin will cure, which causes the crack to become invisible. Most chips or cracks can be mended effectively in this way. This technique can mend tiny chips, along with bigger spider's web type chips. If a hole has appeared in the windscreen, or the chip has expanded too much, you should opt for windshields replacement.
Remember that in windshield repair, it is important to act as soon as possible. When a single chip is left alone, it could spread to a crack or worse, you could end up having to replace the entire windshield. Also, whether you are doing it yourself or having it repaired in a shop, always inspect it so you can be sure that the damage is taken care of.