Say what you're going to talk about. After you've said your own name, just give your audience an idea of what your presentation will be about. This should be no longer than one or two sentences, unless your teachers expects more from you. Once you say your name, you can just say, "Today, I'm going to talk about the life and achievements of Martin Luther," or "I'm going to discuss the importance of a constitutional republic."
This part depends on your teacher. How much detail does she want you to give? One or two sentences should be enough to kick off your presentation, but if she wants you to give a more detailed description of your presentation, then you can add a few more specific sentences to the end of your introduction.