Connecting your interpretation to previous work by other historians:
Once you have a topic in mind, you need to find out what other scholars have written about your topic. If they've used the same sources you were thinking of using and reached the same conclusions, there's no point in repeating their work, so you should look for another topic.
Most of the time, though, you'll find that other scholars have used different sources and/or asked different questions, and that reading their work will help you place your own paper in perspective. When you are writing your paper, you will cite these historians - both their arguments about the material, and also (sometimes) their research findings.
Example: "As Tera Hunter has argued concerning Atlanta's laundresses, black women workers preferred work outside the homes of their white employers"(and then you would cite Hunter in a footnote, including page numbers).
Adapted from: Brown, "Writing about History."