The very first things are the diagrams the assignment demands. So try to begin with them first.
You will notice that you will have to make assumptions for your decisions. Write them down somewhere - all of them!
After you've finished the diagrams
you should compile a text file in which you explain your assumptions. You can do it in one monolithic file or per diagram, thats your choice. Then render it in HTML and upload it. That's all!
HTH,
Harbo