You can either create a new Stage, add your controls into it or if you require the POPUP as Dialog box, then you may consider using DialogsFX or ControlsFX(Requires JavaFX8)
For creating a new Stage, you can use the following snippet
@Override
public void start(final Stage primaryStage) {
Button btn = new Button();
btn.setText("Open Dialog");
btn.setOnAction(
new EventHandler<ActionEvent>() {
@Override
public void handle(ActionEvent event) {
final Stage dialog = new Stage();
dialog.initModality(Modality.APPLICATION_MODAL);
dialog.initOwner(primaryStage);
VBox dialogVbox = new VBox(20);
dialogVbox.getChildren().add(new Text("This is a Dialog"));
Scene dialogScene = new Scene(dialogVbox, 300, 200);
dialog.setScene(dialogScene);
dialog.show();
}
});
}
If you don't want it to be modal (block other windows), use:
dialog.initModality(Modality.NONE);