There is no training required to buy guns in CA. You have to get a firearm safety certificate (FSC), which requires passing a multiple choice test, but no training. I haven't seen this test myself (I'm not a gun person) but I've heard it described as basically trivial, that anyone with some common sense could pass it with no study whatsoever. That sounds much easier than the multiple choice test for a drivers license, which millions of people have passed with no formal training. It does (for real) require some study, but you read the DMV drivers' license booklet, take a few online practice tests, get mom or dad or another driver to explain anything that confuses you, and take the test multiple times if you don't pass on the first try.

Training (16 hours of professional instruction iirc) is required to get a concealed carry permit in my county, but that's a different level than just buying guns. I think other counties just give you the permit if you don't have obvious issues preventing them.