It only takes a pebble to crack a piece of glass. A crack in glass will continue to spread like a spider web until it destroys your entire piece of glass. You may be able to delay repairing a home window, but with a cracked windshield, your car will not pass a safety inspection.
Determine whether the crack is too big to repair. Typically, you can repair a crack that is smaller than the palm of your hand. If the crack has spread farther than that, you need to buy a new sheet of glass.
Purchase a Windshield Pro Glass Repair Kit (see resources). This kit gives you the same tools that a professional would use if you asked one to fix your windshield. The kit costs less than $5.
Squirt window cleaner on the glass and clean both sides of it. Use your paper towels to wipe the dirt and cleaner off the glass.
Read the directions completely on the Windshield Pro Glass Repair Kit.
Squirt the resin into the cracks. Start in the center of the crack and work your way out.
Apply your bridge to the crack. It is the piece that looks like a suction cup. Use the metal bar to tighten the bridge in to place.
Remove the bridge and use a glass scraper to scrape off excess resin. This won't be too hard to remove, so do not apply too much pressure.
Clean the windshield one more time.