In the state of California, all drivers are required to have liability coverage, which pays for injuries or other damages that you cause to other drivers. You are required to have a minimum of $15,000 in bodily injury liability coverage for the death or injury of any one person and $30,000 for death or injury to multiple people (this money is then shared by the affected parties). You are also required to have a minimum of $5,000 in property damage liability coverage to pay for damages you cause to the property of other drivers.
This is the law, but this doesn’t mean that everyone follows it. If another driver does not have any coverage, or enough coverage to cover the costs of the accident, you can sue that person for the additional costs, which then would have to come out of their own pockets. However, if the other driver does not have the money to pay you out of pocket, uninsured motorist coverage (UMC) or underinsured motorist coverage (UIM) can be your saving grace. In the state of California, the insurance companies are required to offer you UMC and UIM, but you have the choice to buy it or not. For more information on California insurance law, the California Department of Insurance is a great source.