Don't understand what to do for the challenge.

// This enum was defined for us with these two cases.
enum Button {
    case Done(String)
    case Edit(String)

    // In the second step we create this method so that we can call it against the done object.
    func toUIBarButtonItem() -> UIBarButtonItem {  // This method will return a UIBarButtonItem
        switch self {  // We are switching on our own object cases.
        case .Done(let value):  // Here we are passing the assigned value in as the value variable.
            return UIBarButtonItem(  // This is the return item for our function.
                title: value,  // This is the string we set when we created our done object.
                style: UIBarButtonStyle.Done,  // This case uses the Done button style.
                target: nil,
                action: nil)
        case .Edit(let value):  // Again we are passing the assigned value in as the value variable.
            return UIBarButtonItem(  // Again we will return this item for the Edit case.
                title: value,  // Using the value string passed in to set as the title.
                style: UIBarButtonStyle.Plain,  // This case would use the Plain button style.
                target: nil,
                action: nil)
        }
    }
}

let done = Button.Done("Done")  // In the first step we create this object.
let doneButton = done.toUIBarButtonItem()  // In the second step we call this method on the object.