java – How can libGDX add buttons and add functionality?

I have developed a game with a libGDX game engine. I want to create a button on the game screen and add a popup to this button. How can I do this?

My current code:

public class GameScreen extends BaseScreen implements ShowDictionaryEvent 
    private Preview preview;
    public GameController gameController;
    public Dial dial;
    private BoardView boardView;
    public DialAnimationContainer dialAnimationContainer;
    private LevelEndView levelEndView;

    private Rocket rocket;
    private BombDialog bombDialog;
    public AlertDialog bombBlastDialog;

    public ExtraWordsButton extraWordsButton;

    private ImageButton shuffleButton;
    private BoardOverlay boardOverlay;
    private Feedback feedback;

    private DictionaryDialog dictionaryDialog;
    private BonusWordsIncompleteDialog bonusWordsIncompleteDialog;
    private BonusWordsCompleteDialog bonusWordsCompleteDialog;
    public SideComboDisplay sideComboDisplay;

    private Smoke smoke;
    private Ufo ufo;
    public boolean offeredBoosterInThisLevel;
    public int nextBoosterType;
    private Label goldPackBubbleLabel;

    private RemoveAdsDialog removeAdsDialog;
    public Image comboLight;;
    public CameraShaker cameraShaker;

    private DelayAction comboLightDelay;
    private SequenceAction comboLightSequence;
    private RunnableAction comboLightRunnableAction;
    public int tempComboReward;

    public GameScreen(KelimeGame wordConnectGame) {

    public void show() {;



        dialAnimationContainer = new DialAnimationContainer(KelimeGame.resourceManager);

        cameraShaker = new CameraShaker();

        gameController = new GameController();