The notorious DMV.
If you don't have a US driver's license, you need to go to the DMV to get your driver's license.
Getting an appointment for the exam is difficult, you can do from here.
https://www.dmv.ca.gov/portal/dmv/dmv/appointments
But because usually takes months just to get an appointment, I would recommend you to go there without appointment in the early morning, and wait in the que (this is for the paper test. For over the wheel, you need an appointment)
To get ready for the paper test, I recommend that you watch this video to understand the basics. This is a walk through guidance of the basics.
https://www.youtube.com/watch?v=E9H0yON1Xf0&list=PL2F4E872DBDFF6AFA
Actual test questions and answers are here.
Good luck with DMV!