how to pop up a window using Ajax control Model pop up extender control

I have a doubt........on my page there is button called "Submit for Approval"( parts.aspx)

| when this is clicked a popup window should open called comments window

in that they can add comments and attachments after -------> once clicked "submit" button the popup closes and the comments entered in that popup window should be seen in read only in parts.aspx page [ there is a textbox in this page and comments should be displayed in the textbox for read-only format