Javafx changing from one scene to another.

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


public class ChangingScene extends Application
{
    public static void main(String[]args)
    {
        Application.launch(args);
    }
    @Override
    public void start(Stage primaryStage)
    {
        StackPane root = new StackPane();
        Scene next = new Scene(root,600,400);//first scene
        
        Button nextBtn = new Button("next");
        root.getChildren().add(nextBtn);//adding nextBtn button on stackpane of scene 2
        
        //creating scene2
        StackPane sp = new StackPane();
        Scene back = new Scene(sp,600,400);
        
        Button backBtn = new Button("back");
        sp.getChildren().add(backBtn);
        
        //adding actions to buttons
        nextBtn.setOnAction((ActionEvent t) -> {
            primaryStage.setScene(back);//on clicking the button next on scene next it ushers you to scene back
        });
        backBtn.setOnAction((ActionEvent t) -> {
            primaryStage.setScene(next);//on clicking the button back it ushers you back to scene next.
        });
        
        primaryStage.setTitle("Changing Scenes");
        primaryStage.setScene(next);
        primaryStage.show();
        
    }

}

Remarks:
This is what happens for example after a successfully verifying that you credentials match those in the database during a login event you are ushered to another scene or page.