Your examiners have to ask you about the significant, original contribution that you put forward in your thesis. They have to do this. They have to ask questions about what it adds to your field, how it’s different and why it’s valuable.
In effect they are asking you, “Why does this matter?” – although they probably won’t say it as simply as this.
Every thesis has a logic to it; you have reasons that bring your ideas together. To start exploring yours just ask yourself why your work matters to you.
What is it about your work that made you want to do it? What did you find and what carried you through long hours and hard work?
It’s a starting point – there are more questions to reflect on that will help you find words to explain what you’ve done to your examiners – but as a starting point it gives you a powerful motivation to say more and explore more.