To register to vote...
Pick up a form at most public libraries, post offices, DMV offices, social service agencies, and at your county elections office. You have to mail in the form to the address specified.
Get a registration form off the Internet at the following address: https://ovr.ss.ca.gov/votereg/OnlineVoterReg
Registration can also easily be done at many tables set up by political campaigns outside supermarkets and other stores prior to most elections.
There is a deadline about three weeks prior to an election when no further registrations will be accepted.