Here you specify the main movie.
Video tracks - click the "Add" button to add the video track of the main movie. You can create a playlist of several movies by adding them one after another. You can also select "All streams" in the "Files of type" field of the open dialog and select all streams at once.
Audio tracks - select the video in the video track list above; you can then add the audio streams of that video. The button text used in the generated menus is shown in <...> - you can change it by double-clicking the item.
Subtitle tracks - select the video in the video track list above and add the subtitle streams of that video here.
Chapters - here you can enter the chapter list in the required format (00:11:22:33 or 00:11:22,789), load it from an external file, or add the chapters directly in the scene editor by clicking the "Edit" button. Note that the chapters are created for the entire playlist.