Specifically on my 66 Mustang, a rundown of registering YOM plates.

DMV YOM Process
https://www.dmv.ca.gov/portal/handboo...

Appendix going over sticker and plate details.
https://www.dmv.ca.gov/portal/uploads...

DISCLAIMER: These videos show my way of doing things. Don't necessarily follow my advice, I could be wrong. You are responsible for your actions. Not me.