After the design is registered, the obligee may apply for examination, and after passing the examination and issuing the certificate, the design right shall have legal effect.
The advantage of certification is that if others use your design without permission, you can take action to stop it. You can only do this if you are certified.
The purpose of the review is to find out earlier similar designs that you want to protect. If the examiner finds that an earlier design is similar to yours, then you can't pass the exam, even if you apply for the design yourself.