It is quite a good idea to repeat the gist of a question in order to involve the audience in the question and to give yourself a little time to think. If you don't know the answer to a question the best course is to say so. Experienced presenters sometimes leave gaps in what they cover in order to prompt questions. A presentation should fit the time allowed for it. You can only learn this by experience or by rehearsal.
Fluent performance is the icing on the cake.
A presentation can still make its point even if you are nervous. Jokes are dangerous. From everything above, you can see that preparation is essential. Your project supervisor should be present at both your mock presentation and the real thing and will provide comment on your proposals for your presentations before you make them and feed-back after your mock presentation. The mock presentation is a learning experience.