When a switch is flipped or a button is tapped in an interface, a controller responds to the interaction. The controller is the brain behind your interface. And like a brain, the controller needs to be properly wired to work correctly.
For the controller to do its job, it needs to know about both the button and label you’ve added to the interface. Right now, the controller is a blank slate, so you need to tell it about the button and label, or outlets. In addition, you need to define the methods, or actions, that will be called when the button is pressed and released.
A controller connects your interface with the rest ...