"Request Flow", how an open cart page is built?

Hello everybody,
I'm sorry but I've not been able to think about a better title.
Anyway the question is pretty simple (hopefully the answer as well), how the MVC generates the page you request?

I'm using OC 1.5.1 and I'm trying to achieve something similar to the Banners functionality (System > Design > Banners) but I need one more step, after the image is (uploaded) selected I need to select some areas of the image and store those coordinates in the db. I thought of one more button next to the Remove one to link to a page where the image is displayed and some javascript will let me do the job. The problem is I'm really clueless about how to create a new page...

Thanks
A.