There's only 2 harbors in OC, Newport and Dana Point
, NP is busy place, takes a long time to get out of the harbor, and you can learn to dodge fast moving ferry
boats in a narrow channel. DP not so busy, shorter distance to harbor mouth, and traffic dodging is usually more SUP's, rental kayaks and PWC's. OCC is well regarded and has extensive range of instruction available. Sailing clubs are an option, there's one in Dana, Aventura, may be some in Newport. There's also Westwind, which teaches at the county sailing center, mostly small boats.
Learn to Sail! | Aventura Sailing Assocication