The XAML part is largely irrelevant - that's defining the layout of your page and the items for interactions. The important bit is in the C# side. Generally, if you're going to just take a quick snapshot from your camera and the camera portion isn't the main part of your application, you're going to want to use the camera capture task.
From memory, it's going to look something like this:
using Microsoft.Phone.Tasks;
using System.Windows.Media.Imaging;
public class CaptureFromCamera
{
private CameraCaptureTask camera = new CameraCaptureTask();
public CaptureFromCamera()
{
camera.Completed += PhotoTaken;
}
public BitmapImage Photo { get; private set; }
public void Show()
{
camera.Show();
}
private void PhotoTaken(object sender, PhotoResult result)
{
Photo = new BitmapImage();
Photo.SetSource(result.ChosenPhoto);
}
}