Many titles provide transcripts (look at the tabs in the box to the right) which can be helpful when citing. Some also allow searching within a transcript to more easily find relevant information, however you need to scroll through the transcript to look for highlighted terms. It does not automatically jump to them.
You can search for your topic or browse. A search is likely to find segments related to your topic, possibly including some from unexpected subjects, but many may be short. Your browsing results are likely to be fewer but lengthier. To browse, choose the menu in the upper left. Then choose subject index, History, American History, Civil War & Reconstruction. You might also find relevant titles in the other history subjects (biography, military history), depending upon your topic.
Take note of the type of film. Your results may include feature films and dramas which are not likely to be acceptable for historical research.