Setting the Layout Manager

FlowLayout() will position the two buttons nicely within the area of the frame.

import java.awt.*; 
import java.awt.event.*;
import javax.swing.*; 

public class TwoButtons extends JFrame implements ActionListener
{
  JButton redButton ;
  JButton grnButton ;

  // constructor for TwoButtons
  public TwoButtons()                           
  {
    redButton = new JButton("Red");
    grnButton = new JButton("Green");

    // choose the layout manager
    getContentPane().setLayout( new FlowLayout() );

    getContentPane().add( redButton );                      
    getContentPane().add( grnButton );
  }                      

  . . . . more code will go here . . . . 

  public static void main ( String[] args )
  {
    TwoButtons demo  = new TwoButtons() ;
        

    . . . . more code will go here . . . . 
    
    demo.setSize( 200, 150 );     
    demo.setVisible( true );      

  }
}

. . . . more code will go here . . . .