To buy a firearm in California, you need to follow specific procedures and requirements set by the state’s laws. Here is a general outline of the steps to purchase a firearm in California:

1. **Check Eligibility**: To purchase a firearm in California, you must meet certain eligibility criteria, including being at least 21 years old, passing a background check, and not being prohibited from owning firearms due to certain criminal convictions or mental health issues.

2. **Obtain Firearm Safety Certificate (FSC)**: Before purchasing a firearm, you need to obtain a Firearm Safety Certificate (FSC) by passing a written test on firearm safety. The FSC is valid for five years and is required to buy a firearm.

3. **Choose a Licensed Firearms Dealer**: Purchase your firearm from a licensed firearms dealer (gun store) in California. It is illegal to buy a firearm from an unlicensed seller in the state.

4. **DROS Process**: When you buy a firearm from a licensed dealer, you will need to complete a Dealer’s Record of Sale (DROS) form. This form collects information about the buyer and the firearm being purchased and initiates a background check.

5. **Background Check**: The licensed dealer will submit the DROS information to the California Department of Justice (DOJ) to conduct a background check. If you pass the background check, you can proceed with the purchase.

6. **10-Day Waiting Period**: In California, there is a mandatory 10-day waiting period between the purchase of a firearm and when you can take possession of it. This waiting period allows for additional background checks and processing.

7. **Pick Up Your Firearm**: After the 10-day waiting period, you can return to the licensed dealer to pick up your firearm. You will need to show a valid California Driver’s License or ID card and sign some paperwork to complete the transfer.

California has an approved DOJ gun roster, please verify that your firearm is approved and on the roster before making your purchase. 

It’s important to note that California has strict gun laws, and additional requirements may apply depending on the type of firearm you are purchasing. It is advisable to familiarize yourself with California’s firearm laws and regulations or consult with a legal professional if you have any questions or concerns.