You can add an object to a panel in several ways, as follows:
From the panel popup menu
Right-click on a vacant space on a panel to open the panel popup menu. The panel popup menu contains an Add to Panel submenu. The Add to Panel submenu enables you to add the following objects to your panels:
Panel applications in the following categories: Accessories, Amusements, Internet, Multimedia, Utility.
Buttons for quick access to common actions: Find Files button, Force Quit button, Lock button, Log Out button, Run button, Screenshot button, Show Desktop button.
Launchers
Launchers from menus
Main Menu
Menu Bar
Drawers
From any menu
When you right-click on a launcher in any menu, a popup menu for the launcher opens. You can use this popup menu to add the launcher to a panel.
You can also drag menus, launchers, and panel applications from menus to panels.
From the file manager
Each launcher corresponds to a .desktop file. You can drag the .desktop file onto your panels to add the launcher to the panel.