Upon finding out your topic.....
Quickly think of 3 main points that you want to emphasize.
If possible, write them down on a sheet of paper as quickly as you find out about your topic
Introduction
* Begin with a short anecdote relating to the topic if possible.
* Briefly mention the 3 main points that you will talk about. Be specific about your main points. Say, "1,________", "2, _________", and "3, ________" Or you can say "First, _____", "Second, ______" and "Third, ________". This will give your speech structure and help your students and your teacher easily follow your speech. Plus, it will serve as guidance for yourself.
Body of speech
1st point: State the first point and elaborate a bit. Incorporate an example if possible.
2nd point: [Same as above]
3rd point: [Same as above]
Try give clear indications that you are starting a new thought or focusing on a new main point. Ex: "Second of all, __________ (insert second main point)
Conclusion
Restate the topic of your speech. Additionally, quickly restate your 3 main points in a similar fashion as your introduction (listing them, but in a conversational way).
As for your audience, if they're students they are generally spacing out during your presentation. Don't be worried if they are giving you dead expressions. It's not because of your performance. They're generally bored.