Confused with a simple example of paging and panning. Obj-C - ios

Question

Studying iOs Development by - The Big Nerd Ranch Guide" (Conway and Hillegass)
Chapter "Subclassing UIView and UIScrollView"; Panning and paging.
The following chunk of code being typed in the
- (BOOL)application: didFinishLaunchingWithOptions: method.
(HypnosisView - is a custom made class that actually performs the drawing on the screen.)
Can't understand following code:
self.window = [[UIWindow alloc] initWithFrame:[[UIScreen mainScreen] bounds]];
//-------Adding a scrool option-----------
CGRect screenRect=[[self window] bounds];
// create the UIScrollView to have the size of the window, matching its size
UIScrollView *scrollView = [[UIScrollView alloc] initWithFrame:screenRect];
[scrollView setPagingEnabled:YES];
[[self window] addSubview:scrollView];
// create the HypnosisView with a frame that is twice the size of the screen (with a big
// width)
CGRect bigRect = screenRect;
bigRect.size.width *=2.0;
HypnosisView *view=[[HypnosisView alloc] initWithFrame:screenRect];
// add the HypnosisView as a subview of the scrollView istead of the window
[scrollView addSubview:view];
// move the ractangle for the other HypnosisView to the right, just off the screen
screenRect.origin.x = screenRect.size.width;
HypnosisView *anotherView = [[HypnosisView alloc] initWithFrame:screenRect];
[scrollView addSubview:anotherView];
// tell the scrollView how big its virtual world is
[scrollView setContentSize:bigRect.size];
So our goal is to create a view instance with an width bigger than the iphone screen.
First we are declaring new variable "screenRect" that has bounds of a "window".
Then we are creating an instance of "UIScrollView" that has frame dimensions same as the
"screenRect" same as the window.
Making paging enabled.
Adding our newly created "scrollView" to the hierarchy of views.
So we have parent "window" and child "scrollView" (that has same dimensions as our main window)
Declaring a new variable "bigRect", and making it equal to our previously declared "screenRect".
Setting bigRect's "width" property to be twice as much.
Creating a new "view" object that is an instance of our custom made Hypnosis class that actually performs the drawing. We set our view's frame to be the same as our "screenRect" frame.
Adding our newly created "view" to the hierarchy of views. Now we have 3 level hierarchy: UIWindow--> UIScrollView-->HypnosysView
9.Now here, I don't understand what this line of code does and why do we need it (screenRect.origin.x = screenRect.size.width;)
10). Why are we creating another instance of HypnosisView in the next line?
11). at the end we notify scrollView about how big its size.

Answer 1

9.Now here, I don't understand what this line of code does and why do we need it (screenRect.origin.x = screenRect.size.width;)
10). Why are we creating another instance of HypnosisView in the next line?
The example will display 2 HypnosisViews which are side by side in a scroll view. The second one is off screen. So you have to drag/page the scroll view to see it.
screenRect.origin.x = screenRect.size.width
This just positions the 2nd hypnosis view to the right of the fist one.