First of all DON'T PANIC, you're going to be okay.
Second, take a look at the links the above posters mentioned to see the criteria of the award and look at some of the ideas that have been submitted successfully in the past.
Third, think about the story of your team. When did you start your team, where did your team begin, who started your team, etc etc etc. Essentially give a brief team history.
Fourth, what obstacles have you overcome as a team. This can be anything from having trouble recruiting students, to not having enough funds, to not even having a build space or any tools. Every team has had challenges in the past, even if you think they weren't that bad. Judges love to see teams that persevere despite adversity.
Fifth, describe how your team fulfills the goals of FIRST. What outreaches have you done, how do you interact with your community, how do you inspire those around you to learn more about science and technology...all that sort of stuff.
Lastly, explain what makes your team special. It could be a weird tradition you have, a unique way of working together, or just something that you think makes your team different.
After you've done all that you should have a fairly large body of text to work with and you can add or subtract what you need from there. The best thing to remember about Chairmans is it's a chance to brag about your team and what you've done together. It's an opportunity to showcase everything you've worked on and maybe even get some recognition from it.
Good luck, and remember to have a little fun with it, it makes life a lot easier.
