I am studying Xcode from the official apple website and it explain how to merge ui elements with the button "stack view" , I have the latest version of Xcode, but I can't find this button, how I can create a stack view or similar thing?
From the official doc:
In the first pages of this Tutorial where it seems that you got the image, there is a screenshot with the XCode Logo with a "Beta" sign.
UIStackView are introduced in iOS9.
So it can only be used with an XCode that supports iOS9 (currently in Beta): XCode 7 (Beta).
Even if you could use the iOS9 SDK in XCode 6, I think that it wouldn't have the "Stack View" Button. Maybe Apple will give a last update to XCode 6 to supports iOS9, but that is just speculation.