Do I need a appointment to know much i owe plates for my car?

No

No, you can use the free registration calculator on the California DMV website. Here is the link: https://www.dmv.ca.gov/portal/dmv/?1dmy&urile=wcm:path:/dmv_content_en/dmv/portal/feecalculatorweb/index

I believe so, they will need to access the system and for that you will need to get a number. If is the sticker you are referring to then you can use the machine for that, just bring your old registration and it will tell you how much you owe.