they want us to convince them why they should chose me)
Sounds like you need to make an argument that the final outcome will be better if you go to this school rather than another school. Maye this is because you have a big plan for your time at this school, involving a particular club or professor.
You also have to show that other people will benefit by your attending this school, rather than some other student attending the school. Why will the world be better served by you attending than someone else?
It all comes down to a question of what actual, real-world difference will be made by you attending this school. What will be different about your life if you attend (name of some other school) instead of this one? Tell them a story that involves you giving back to society or contributing to your field DURING your time at this school and/or after graduation. You have to identify what makes this school unique in order to identify the difference that will be made by you attending it instead of another school.
Convince them that the way in which the school is unique and the way in which your plan is unique (and you must have a real plan) are related in some significant way. :-)