Research Papers / Trouble narrowing a topic on the Vietnam war [3]

I just can't seem to get the idea of narrowing a topic but not making it too limited. Actually, the whole idea of the research paper escapes me. Still, I want to try. If one is assigned a genreral topic like the vietnam war how does one narrow it without limiting it oo much especially if it's not a subject one knows anything about nor is interested in? How about if the assignment topic is a person but the instructions say don't give me a bigtaphy. I could use help specifically with both these topics and in general with the idea on how to narrow and then what. I've never written a paper before. I am 50. Thank you for taking the time to read this. What a wonderful resource.