When your car insurance is cancelled it means you're no longer being covered by the insurance company and you legally have no car insurance on your vehicle.
So to legally drive your vehicle you need to get car insurance again either through the same company by having them reinstate the car insurance or if they won't reinstate the car insurance you'll need to shop for other car insurance coverage.
If you get stopped without auto insurance then you could get fined or have your car towed away which can cost you more than the car insurance.
Sometimes your car insurance may be cancelled due to non payment and in that case usually making the payment will get your auto insurance reinstated again.
If its because of something else then you'll need to go to another car insurance company and get auto insurance coverage through them.
Until then you're not insured and can get into trouble for no car insurance.