You can add the following types of menu to your panels:
System menus: System menus contain the standard applications and tools that you can use in your desktop environment. The Applications menu and Actions menu are system menus. To add a system menu to a panel, right-click on a launcher in the menu, then choose Entire menu -> Add this as menu to panel.
GNOME Menu: You can access almost all of the standard applications, commands, and configuration options from the GNOME Menu. To add a GNOME Menu to a panel, right-click on any vacant space on the panel, then choose Add to Panel -> GNOME Menu. You can add as many GNOME Menu objects to your panels as you want. By default, the GNOME Menu is represented on panels by a stylized footprint icon, as follows:
Menus that you add to your panels are represented by an icon with an arrow. The arrow indicates that the icon represents a menu or drawer. Figure 4–4 shows how menus typically appear on panels.