Categories Vs. Forms

So Im trying to differentiate the Forms from Plato and Categories from Aristotle from each other to get a better grasp. From what I can gather the difference is that the Forms explain that there is an essence of each form that makes it a form and what we know as interpretations of those forms. In Aristotle's view, what makes up a category is not the "essence" like in forms, but it is a collective force that makes the category what it is. Because of the several things that make up a category makes it a category. So in Aristotle's view its not essence that makes up a form or something, but the collective-ness of what is made of it that makes it something. I'm not sure if this is right but Im just typing out my thoughts as I think them =/.  Another difference that I am gathering, is that Plato thought the Forms made up everything that was smaller, or everything that resembled a form, and Aristotle figured that everything that was a Form or a Universal, or Category made up the big, or the whole. So it was kind of backwards and they both clearly opposed each other on the views of Absolutes.