sales order form

I should create a form which is related to sales order subform with fields like type, no, quantity, qty to ship. This form should attach to the menu items in the sales order. My condition is that when I press the menu item in sales order I should see the form and when I enter values in that form and press ok menu button then it should automatically update in sales order sub form with the values entered in the newly created form...please explain the process how to write code and where to write..? I am using classic client 2009 r2.