In CA, what is the process to replace license plates?

I was pulled over for not having my front license plate, so I need two brand new license plates. I understand there is a form I have to fill out and send in to the DMV, but someone told me that I shouldn’t go to the DMV because it is a waste of time when you just have to send the paperwork over and all the DMV would do is pass the paperwork along. I know that new plates cost money, but if you’re just sending in the paperwork do they bill you later? Gah. This is so confusing! Has anyone been through this and know the steps?

To make matters a bit more confusing, I have to go get my smog check and send in THAT information so I can get my registration stickers.