Hi there Michelle.
The Propsal is a short (mine was one page) document formally listing your main question: eg: "How have historians treated the Sonderweg thesis?" and two sub questions: eg: "How has historian AJP Taylor treated the Sonderweg thesis". Additionally, your proposal should contain a general description of your methodology till now, so how you arrived at your subject/question but also how you intend to continue your research. This description should inculde the type of sources you intend to use (and have used thus far).
Also, this will most likely be the first time you have written anything formal for the course so don't worry to much, after all its only 5% of the overall major work.
Good luck...