In order for you to file a car insurance claim in the state of California, you must notify your insurance provider. This can be typically done through the phone, web, or, or even through a mobile app.
It doesn’t matter whether you or the other driver was at fault. If you already have an insurance policy, you must notify your provider. If you are uninsured, you may also file a claim with the other individual's insurance provider, but only if they were totally or partially at fault.
If you were injured in a car accident, it is always best to retain a car accident attorney before speaking with your provider. Insurance companies, even your own, are designed to look after their own interests. Their main interest is maximizing profits, even if it is at your expense.