I always found that if I could describe a subject to my missus, before she fell asleep or told me to p*ss off then I was along the right lines.
For structure, just use an example of any subject from your instructor doing the FIC course as a starting point.
Most subjects can be broken down into:
1. What you are going to talk about.
2. The details
3. Summary and any questions.
The main thing is to practice, it get's easier and eventually you will develop your own style.
Unfortunately, once you get a job you won't generally get to do much briefing anyway.
Enjoy the course.
FIS.