Voting in California and Beyond (No Book)

At our last meeting, a couple members said they'd like to meet to discuss the June 2 primary elections. Primaries? What's up with these? How do they work? Are Democrats splitting a vote for governor in a way that seats a Republican by default? Hopefully someone in the group can find a link and enlighten us all! Here's a link to a San Diego ballot.
https://drive.google.com/file/d/1Udvf0j-XiLH4uYrUrwQn9dDdxjZGC68P/view?usp=sharing

We can broaden the subject, too, to the recent gutting of the Voting Rights Act, prospects for the November midterms, and related topics. If you have any good articles on the primaries, candidates or related national topics, please leave them in the comments section. I will add some too. Thank you!