In JavaFX, the StackPane class is a layout container that arranges its child nodes in a stack, where each child node is positioned on top of the previous one. You can use it to create layered UIs, where the topmost node is the most visible one.

Here's an example of how to create and use a StackPane:

import javafx.application.Application;
import javafx.scene.Scene;
import javafx.scene.control.Button;
import javafx.scene.layout.StackPane;
import javafx.stage.Stage;

public class MyJavaFXApp extends Application {

    @Override
    public void start(Stage primaryStage) {
        // Create a StackPane object
        StackPane stackPane = new StackPane();
        
        // Create some child nodes and add them to the StackPane
        Button closeButton = new Button("Close");
        closeButton.setOnAction(e -> primaryStage.close());
        stackPane.getChildren().add(closeButton);
        
        Button helpButton = new Button("Help");
        stackPane.getChildren().add(helpButton);
        
        // Create a scene and set it on the stage
        Scene scene = new Scene(stackPane, 300, 200);
        primaryStage.setScene(scene);

        // Show the stage
        primaryStage.show();
    }

    public static void main(String[] args) {
        launch(args);
    }
}

In this example, we create a StackPane object and add some child nodes to it, such as Button objects. We use the getChildren().add() method to add the child nodes to the StackPane. The order in which we add the child nodes determines their stacking order, with the last added node being the topmost one.

When the user clicks the "Close" button, we call the close() method on the primaryStage object to close the window.

The StackPane is a simple yet powerful layout container that enables you to create layered UIs with minimal effort. It's often used in conjunction with other layout containers, such as GridPane and BorderPane, to create more complex layouts.