The viva is an oral exam at the end of your PhD. Typically two examiners study your thesis and prepare for a discussion with you centred on your work and ability as a researcher.
You’ll have plenty of time to prepare. Vivas happen to others all the time, so there’s lots you can learn about the process. This helps you prepare too.
Through all of this you can be ready for the time you’ll spend talking with your examiners. Viva candidates most commonly pass their viva.
You will too.