Filing a California mechanics lien is a relatively simple process. Generally, a lien claimant must simply fill out a California mechanics lien form, send or bring that document to the county recorder for filing (and pay a fee to have it recorded), then provide notice to the property owner that the mechanics lien was filed.
There are a lot of little details to consider, though - like what information should appear on the lien document and where, exactly, that lien should be filed. This article provides much more detail than I possibly could here: How to File A California Mechanics Lien – Step By Step Guide.
For more background on California's mechanics lien rules, these resources are helpful too:
(1) California Mechanics Lien Guide and FAQs(2) California Preliminary Notice Guide and FAQs