I remember in Xcode 3 there was "Debug", "Release" and possibly "Distribution". There was a dialog where we could duplicate the "Release" build config and rename it to "Distribution" in order to modify some build settings for distribution.
In Xcode 4 I can't find references to these Build Distributions as known from Xcode 3. When I click on my project in the navigator, I get a big window on the right. There I click "Build Settings" and choose the "All" filter along with "Levels".
It shows me these columns: Settings, Resolved, AppName, AppProject, iOS Default.
It seems that they compressed all the different configurations into this massive list. Many build settings show up in different "flavors". For example: Architecture > [Debug | Distribution | Release].
On the other hand, other build settings don't appear splitted up into these 3 "Build Configuration types". For example there is just one Base SDK setting (despite the fact that it would be nonsense to set different Base SDK for different Build Config. Or maybe not.)
Unfortunately the iTunes Connect integrated help system is still hanging around in Xcode 3 good old days and telling me to duplicate a Release build config. Which I can't in Xcode 4.
The iOS App Development Workflow Guide does not go into detail about HOW to actually DO it in Xcode 4. Only about three paragraphs on that page refer to building for the App Store. It mentions an "AppStore Scheme" which I don't even have, since I did not create my project with Xcode 4 initially.
Best Answer
In the left sidebar, click on your project, then in the window to the right click on your project name. And there are your configurations, in the Info tab of the main window.