But example 5 does not show how to get the option that the user chose.
There are 2 possible options in the list box in example 5, which are "File open" and "Window created".
If the user clicks on window created, how can I know?
What should I do in the event receiver?
You catch the event (EGET_LISTBOX_CHANGED and EGET_LISTBOX_SELECTED_AGAIN for listboxes) in your eventreceiver and act on that. And previews are mostly 2d-images, although in RPG's for example you also often see real 3D models (probably using render-to-texture).
if (stringw(listBox->getListItem(listBox->getSelected())) == stringw(L"ABC"))
Or instead of converting to Irrlicht strings, you can use strncmp from the C standard library. It's designed to do string comparisons between C-style strings.