import javax.swing.JFrame;


public class MainApp 
{

    public static void main(String[] args) 
    {
    new MainApp().start();
    }
    public void start()
    {
         CalculatorUI obj = new CalculatorUI();
         obj.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
         obj.setSize(275,275);
         obj.setVisible(true);
    }

}

import java.awt.FlowLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JOptionPane;
import javax.swing.JTextField;


public class CalculatorUI extends JFrame
{
    //Variables.
    private JTextField text1;
    private JButton button1;
    private JButton button2;
    private JButton button3;
    private JButton button4;
    private JButton button5;
    private JButton button6;
    private JButton button7;
    private JButton button8;
    private JButton button9;
    private JButton button0;

    public CalculatorUI()
    {
        super ("Calculator");
        setLayout(new FlowLayout());

        text1 = new JTextField(10);
        text1.setEditable(false);
        button1 = new JButton("1");
        button2 = new JButton("2");
        button3 = new JButton("3");
        button4 = new JButton("4");
        button5 = new JButton("5");
        button6 = new JButton("6");
        button7 = new JButton("7");
        button8 = new JButton("8");
        button9 = new JButton("9");
        button0 = new JButton("0");



        theHandler handler = new theHandler();
        text1.addActionListener(handler);
        button1.addActionListener(handler);
        button2.addActionListener(handler);
        button3.addActionListener(handler);
        button4.addActionListener(handler);
        button5.addActionListener(handler);
        button6.addActionListener(handler);
        button7.addActionListener(handler);
        button8.addActionListener(handler);
        button9.addActionListener(handler);
        button0.addActionListener(handler);

    }
    private class theHandler implements ActionListener
    {
    public void actionPerformed(ActionEvent event)
    {
        String string = "";


        if(event.getSource() == text1)
        {
            string = String.format("Field1: %s", event.getActionCommand());
        }
        else if(event.getSource() == button1)
        {
            string = String.format("Field2: %s", event.getActionCommand());
        }
        else if(event.getSource() == button2)
        {
            string = String.format("Field3: %s", event.getActionCommand());
        }
        else if(event.getSource() == button3)
        {
            string = String.format("Pasword Field: %s", event.getActionCommand());
        }

        JOptionPane.showMessageDialog(null, string);
    }
    }


}

Where do you add any buttons to the GUI container object?

How do you do that? I have another tutorial on my Hd and there doesnt show any code of adding the Buttons.

Here's another tutorial re GUI
Click Here

Use the add() method to add components to a container.

How do you do that? I have another tutorial on my Hd and there doesnt show any code of adding the Buttons.

am i putting that in the Main or the UI class ?

Take a look at the tutorial on how to build a GUI

am i putting that in the Main or the UI class ?