The glass is still there
A windshield is laminated — two layers bonded to a plastic interlayer. When it fails it goes opaque with cracks but stays in one piece and stays in the frame. It does not come into the cabin.
Visibility drops sharply, which is the actual emergency. The glass itself is not going anywhere.
The first ten seconds
Do not brake hard, and do not swerve. Both are the instinct and both are more dangerous than the reduced visibility.
Ease off the accelerator, put the hazards on, hold your lane, and let speed bleed off. If you can still see through part of the glass, use it. If you cannot, the driver's side window is your reference — lower it and use the lane line and the shoulder.
Move right progressively and get onto the shoulder or the next exit. Get well clear of the traffic lane before you stop.
Do not punch it out
A common piece of bad advice. The interlayer is what is holding a shattered windshield together and keeping it out of the cabin — breaking through it turns a visibility problem into a face full of glass at speed.
Wait until you are stopped and off the road.
Then
Photograph it before anything else, for the claim. Do not drive further than getting off the road — a shattered windshield contributes nothing structurally, and in California driving with obstructed vision is citable.
Call. This is exactly what 24/7 mobile service exists for: we come to where the car stopped rather than asking you to drive it.
Need this done rather than explained? There is no shop to drive to. We come to wherever your car already is — your driveway, your workplace car park, an apartment lot, or the side of the road it stopped on — anywhere in greater Sacramento, with no call-out fee and no mileage charge. Give us the year, make and model and you will have a firm price before the call ends.