Andrea,

For the new GIMP 2.6 the menu bar on top of the toolbox-window was
removed and merged into the other (initially empty) window. So the
other (empty) window has all of the menu items. The menu items now
also contain stuff like File > Open to open an image.

For people who are used to working with The GIMP this is a new thing,
but for all other users this is about the way their other software
works (one menu bar with File > New, File > Open, File > Save, etc).

I advise you to read this overview of what is new in GIMP 2.6:
www.gimpusers.com/tutorials/gimp-2-6-new-features.html
The text is in English and the screenshots are from the German
language version of GIMP. But at least these show how GIMP should look
nowadays.

That is a more elaborate article than the GIMP 2.6 release notes:
www.gimp.org/release-notes/gimp-2.6.html

Kind regards,

Martijn
http://gimp.startpagina.nl