In general, if the damage is smaller than one inch in diameter, it usually can be repaired easily. If it is much larger, probably you're better off ordering a new windshield to be installed by skilled technician instead of repairing it, as most of the time the weakened area will eventually give away.If the damage is very small, you can try one of the windshield repair kits available on the market, however its durability compared to repairs performed by professional is still debatable.
If the damage obscures your field of view, repairing the windshield is often a dangerous choice. You should replace the damaged windshield with a new one as soon as possible. It is not a good idea to get a windshield from car junkyard, as it may have small defects and can have very short useful life. Don't take a windshield from a totaled car, because collision shocks and air bag deployment often create excessive stress on the windshield. When buying a new windshield make sure it is an OEM. Choosing a poor windshield could cause serious injury or even death due to an accident.
For this reason, the work should be performed by a trusted windscreen specialist. In many areas, windshield replacement business can do the job anywhere, including in your driveway. If you are unable reach to a repair shop immediately, gently put some adhesive tape over the damaged area to slow the spread down. It is also helpful to drive as slow as possible and avoid bumpy roads. Do not touch the damaged area, try to keep it dry, and don't use air conditioning, heater or defroster, as changes in temperature and humidity can escalate the cracks.