You should start by introducing yourself and thanking them for judging your project. At that point, the judge will probably ask you to describe your project. They will ask you questions pertaining to your project:
- Why did you decide to perform this research?
- What are your findings?
- Would you repeat the experiment, and if so, what would you change?
These are just a few of the questions the judge may ask you.
Above all, however, enjoy the experience of presenting your project to the judge. They are there to help you learn even more from your project, and to applaud your efforts of conducting scientific research.