import javafx.application.Application;
import javafx.fxml.FXMLLoader;
import javafx.scene.Parent;
import javafx.scene.Scene;
import javafx.stage.Stage;
public class FXMLExample extends Application{
    @Override
    public void start(Stage stage) throws Exception {
        Parent root = FXMLLoader.load(getClass().getResource("FXMLDocument.fxml"));
        Scene scene = new Scene(root, 300, 275);
        stage.setTitle("FXML Welcome");
        stage.setScene(scene);
        stage.show();
    }
    public static void main(String[] args) {
        launch(args);
    }
}

<GridPane xmlns:fx="http://javafx.com/fxml" alignment="center" hgap="10" vgap="10">
        <padding>
            <Insets top="25" right="25" bottom="10" left="25" />
        </padding>
      <Text id="welcome-text" text="Welcome" GridPane.columnIndex="0"
            GridPane.rowIndex="0" GridPane.columnSpan="2" />

        <Label text="User Name:" GridPane.columnIndex="0"
            GridPane.rowIndex="1" />

        <TextField GridPane.columnIndex="1" GridPane.rowIndex="1" />

        <Label text="Password:" GridPane.columnIndex="0"
            GridPane.rowIndex="2" />

        <PasswordField GridPane.columnIndex="1"
            GridPane.rowIndex="2" />

        <HBox spacing="10" alignment="bottom_right" GridPane.columnIndex="1"
            GridPane.rowIndex="4">
            <Button text="Sign In"/>
        </HBox>

        <Text fx:id="actiontarget" GridPane.columnIndex="0"
            GridPane.columnSpan="2" GridPane.halignment="RIGHT" GridPane.rowIndex="6" />

    </GridPane>