how do you create popup window using glade3

[frank zhu <frank zhu mingyu gmail com>]

hi,
I am new to GTK+ development and I used glade3 to create my application
window which contains a menu.  If a menu item is activated, I want to popup
another window.
I think the easiest way is to write a callback function to create it in C
code, but is this the common way? or is it possible to create that window
using glade3?

I can provide my source code and glade file if needed.
Thanks,