Hmm, you are in a scene of a storyboard and you want to add a UIScrollView.
Ok, from the utility area add Scroll View object on top of your scene.
If you have already placed UI objects (like labels, textfileds etc), the scroll view will be on top of that.
To overcame this, toy have to move the UI objects from UIView children to UISrcollView children. You can change the order playing with items that are displayed in the Xcode outline view (which is the pane that appears between the canvas and the project navigator).
The following image is illustrative
Thanks to Marino's post to geeky lemon development.