Remember it's a comparison, so...
You must include things that are the same, for example:
Dans mon collège et au collège à Banga Bola il y a des professeurs.
You must also include any differences, for example:
Dans mon collège, il y a des ordinateurs, mais au collège à Banga Bola il n'y a pas d'ordinateurs.
You can also include other things that you've learned this unit, such as your opinions on both schools (including reasons of course!), and what you study and when. Use what you've learned, and not what you find on Google Translate or from parents!
Don't forget it's an informal email, so make sure you include all the conventions of one!
(Remember your feedback from Unit 1's writing assessment)