I am having hard time in learning constraints & auto-layout in iOS.I have used any-widt
The Add Missing Constraints error is shown because you have not provided vertical constraints, may be height constraints or vertical position constraints.
To fix this use the blue dotted guide lines to place your view and then click on "Reset to suggested Constraints" or you can provide the vertical constraints according to your requirement.
Xcode maybe warning you for button width because by default the text label of button takes the default padding space.
To add custom padding you should change the insets of your button contents from the storyboard.