The black rectangle is a preview frame from the clip, and as such is also a button (select it for playback on the final disc). You can set which frame to use in the Edit window by double-clicking a clip in the main window, then using a slider (not very precise, I know), then Set Picture.
It is probably black for you, as the first frame (default) of your clip is black (as it often is).
Alternatively, there are some themes (menu templates) that have no preview frame, like Splash.
The ‘My Movie’ text in the menu, is the menu title. You can edit that with Customize in the right side panel, then the Menus tab.