When I install new software, the menu item on main menu is not created
automatically.
However the new software was successful installed and I can create a
new item on main menu manually (Adding a new item menu and specifying
the location to the command application).
What can I do for the new software instalations automatically create a
item on the main menu?
What Desktop manager are you using ? KDE, gnome?
Anyway, it should be automatic. Try to wait a few second, or try to
disconnect you and login back ,to see if it changes anything.