You can use our samples to get a good overview of how to show the barcode scanner in an app: Run the samples.
The scan view itself (BarcodePicker) is a RelativeLayout and therefore a normal view in Android. You can add it to the view hierarchy like any other view and add further views on top of the overlay view or the picker itself.
Displaying the scan view in fullscreen
To display the scan view in fullscreen the best option is to open an Activity for it and set the barcode picker as the content view.
Adding the scan view as a subview
As the BarcodePicker is a normal RelativeLayout you can add it to your own layout like any other view:
Scaling and/or Cropping the subview
To scale and/or crop the scan view you only need to change its width and height. Here is a small example of scaling the scan view to 3/4 of its width and 1/2 of its height (meaning 1/12 of its height will be cropped at the top and 1/12 at the bottom):