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.
Even if you only drive on surface streets, the occasional rock or piece of debris can hit your vehicle's windshield and leave a mark. If you travel often on the freeways, it can happen much more frequently. If a piece of debris creates a minor chip in the glass, it may not cause a serious problem. However, if a crack develops, it can travel and grow larger. Eventually, it may even become a safety issue. Contact a windshield repair specialist and have the damage fixed.
Test your lights. If you notice an improvement-you are done! If it still appears dim or cloudy, you may want to use a special plastic cleaner and wax to give it a higher polish and sheen. These can be purchased at fix auto glass repair repair stores. When using them, be careful not to get any on the rest of the car as it could cause damage. Some masking tape around the headlight border can help protect it. You may want to use a rotary buffer to ensure the smoothest polish possible.
Once you have figured out that the crack on your windshield can be repaired, you will need a good repair kit. You can get one from your local auto parts shop or online auto parts retailers. Usually, rockchip repair kits come with an applicator or injector, an adhesive curing film, a suction cup (which serves as the base or stabilizer), and a tube of liquid resin.
Most of the technicians have years of experience and are capable of undertaking any type of repairs. Usually they are professionals and not the general car mechanic who lacks expertise on this matter. It all depends on the kind of service provider you are going to. Make sure, it is a reputed one. The glasses of doors, windshields and mirrors can be mended by the skills of the workmen. Some of them are mended so well, that it would be difficult to say that they were once broken. A cracked mirror is said to bring bad luck. So don't have one in your home if you believe in this. Instead get it mended and restore it to its former glory.
Sometimes, the crack in the Auto Windshield glass is very long and unavoidable. In such cases, its better to replace the glass instead of repairing it. The reason is that in the long run it will be more harmful than the crack itself. It might break in the car itself when you are driving because of the stress.