Not everybody in California has an address. Everybody in California is impacted by the laws here, so everybody should vote.
You do not have to have an address to vote. You do need to be able to describe where it is that you stay.
If you are registering via a paper form, use the map on the bottom of the voter registration form, you can identify two cross-streets where you usually stay. If you are registering online, you can check the box that says, “I do not have a street address” in the address section.