If you want to edit the menu manually just follow the link
http://wiki.xfce.org/howto/customize-menuAND pay attention to copying the desired apps *.desktop file to .local/share/applications from /urs/local/share/applications/
Hint from my /home/user/.config/menus/xfce-applications.menu:
snip....
<Include>
<Filename>xfburn.desktop</Filename>
<Filename>xfce4-terminal.desktop</Filename>
<Filename>thunderbird.desktop</Filename>
<Filename>firefox.desktop</Filename>
<Filename>xfce4-about-xfce.desktop</Filename>
<Filename>xfce4-logout.desktop</Filename>
</Include>
<Layout>
<Menuname>Settings</Menuname>
<Separator/>
<Merge type="all"/>
<Separator/>
<Filename>xfburn.desktop</Filename>
<Filename>xfce4-terminal.desktop</Filename>
<Separator/>
<Filename>xfce4-about-xfce.desktop</Filename>
<Filename>thunderbird.desktop</Filename>
<Filename>firefox.desktop</Filename>
<Filename>xfce4-logout.desktop</Filename>
</Layout>
..../snip
You also have to edit the .local/share/applications/*.desktop file and change to this:
Categories=X-XFCE;X-Xfce-Toplevel;
This gives me xfburn, xfce4-terminal, xfce4-about-xfce, thunderbird, firefox and xfce4-logout at top level in the xfce-menu.
Hope this is of help...