dlgAbout extends javax.swing.JDialog {
 
    /**
     * Creates new form dlgAbout
     */
    public dlgAbout(java.awt.Frame parent, boolean modal) {
        super(parent, modal);
        initComponents();
    }
 
    private void btnOKActionPerformed(java.awt.event.ActionEvent evt) {                                      
        // TODO add your handling code here:
        this.setVisible(false);  // close current window
    }
}

In other window or menu, call dialog to open it:

package com.acme.showcase;
 
/*
 * To change this license header, choose License Headers in Project Properties.
 * To change this template file, choose Tools | Templates
 * and open the template in the editor.
 */
 
 
public class frmMain extends javax.swing.JFrame {
 
    public frmMain() {
        initComponents();
    }
 
    //...
 
    private void mnuAboutActionPerformed(java.awt.event.ActionEvent evt) {                                             
        dlgAbout dlg = new dlgAbout(this, true);
        dlg.setVisible(true);
    } 
}