Xfce/Xubuntu Applications Menu is a panel plugin that displays a menu that allows access to installed applications.
The items on the menu can be edited using one tool called Alacarte. Alacarte can be access at Applications Menu > Settings > Main Menu or just type
alacarte in the command line (or in xf4run).
The Main Menu editor has 3 main sections: Menus list (left), Items list (center) and Action buttons (right).
The Menus list sorts applications by category. Each menu can hold items and other menus (a menu has to possess at least one item to be displayed). The available action buttons for menus are "New Menu" and "New Item", and their name is self-explanatory.
The Item list displays the list of application launchers for the selected menu/category. Items can be moved up and down on the list and their attributes (name, command...) can be edited using the "Properties" action. Items can also be hidden from the menu using the "Show" checkbox, next to the item's name.
On bottom of the Main Menu editor's (Alacarte) interface there is a button "Revert" that restores the default menu layout.