If you have an image you want to save, you just need to press the buttons at the top and bottom of the iPhone simultaneously . You'll hear a camera sound and see a flash. The image will be saved to your photo library.
Before you take the image, you might want to pause the simulation, and make sure the toolbar is hidden. To hide the toolbar, just tap the screen once. Tap again t show the toolbar.
Here are a few images I captured recently: