To obtain drivers license, first step is to clear written exam. It is not that simple, you have to score around 85 to 90% to pass exam, ie you are allowed to make only 3 to max 5 mistake in entire question paper. Basically candidate is asked around 30 objective questions. I am sharing this link which is free and best to learn and practice. (I studies with this link and cleared written paper in first attempt)
Please remember, that different states has different questions and pattern. You can pick the state and start pracitce exams http://driving-tests.org/
1. Get the Drivers handbook or manual from DMV office or download it from https://apps.dmv.ca.gov/pubs/dl600.pdf
2. When you are done reading entire handbook start free practice test from website http://driving-tests.org/california/
3. When you start scoring more then 90%, take online appointment and visit DMV office with all your documents like passport, ssn number, visa papers, your current driving license (out of US as well) https://www.dmv.ca.gov/portal/dmv/detail/portal/foa/welcome?localeName=en
4. Once you pass written test they will give you permit (can can only drive with an adult driving license holder), however if you already have a valid out of US DL, in that case you might directly get the temp . driver license (driver independently / alone).
5. Join driving school or rent a car and practice and then appear for field test (behind the wheel driving test) when you are ready by taking online appointment https://www.dmv.ca.gov/portal/dmv/detail/portal/foa/welcome?localeName=en
Best of Luck friends