If you are submitting your App to +Windows Phone site you would require to publish screenshots of your App. These are the snapshots a prospective user might see even before she downloads your App. How to take a good snapshot then ..
Click the Double Right Arrow on right of the Emulator to bring the menu. Now take as many as possible.
See also:
How to Add/Load XAML Dynamically to RichTextBox Control - Windows Phone Development C#/VB.NET