There are two reasons for this assignment. First, it forces you to get an early start on your research project (instead of putting it off to the end of term and then trying to put it together at the last minute...which won't work). Second, the proposal allows me to offer some feedback and advice on your chosen field of investigation.
Finally, the research topic you propose in this assignment is not set in stone. You may discover after a bit more investigation that what you proposed to study is not that interesting after all or that the topic is too broad and needs to be narrowed down. If you decide that you want to change your research topic that is fine, but tell me that you are changing your topic.
Take this link for some ideas about how to get started.