Typically with a UISplitViewController if you want to keep the entire space of the screen usable by the Detail view of your app then you will place the master (controlling) view within a UIPopOver.
The Mail app does things differently by sliding in the detail view from the left.
Keith Harrison has written an excellent tutorial on how to create a UISplitViewController modeled after the Mail app which has a master view that slides in from the left responding to toolbar presses, and to gestures.
A full example project is included.
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