California is quite different from any other state I have visited in the continental U.S. There is diversity in all aspects: topography, language, food, ethnicity.
From my point of view, here is an outline of what you can cover in a week in two major cities—San Francisco and Los Angeles. Consult a guidebook for details. Look up reliable sources online.
A ride from the airport to the city will be expensive, between $45-$75, depending on location and traffic delays. You might want to look into a rideshare option.
Take a conducted tour because it’s an easy way to get to know a city. You can then decide where you would like to spend more time within the cities of San Francisco and Los Angeles.