The toolbar is a small area to display information by fluxbox, like a clock, or buttons for running programs.
It is configured by the init-file and the style-file. Init settings usually are changed by the toolbar menu.
The toolbar can be switched off (made invisible by setting session.screen0.toolbar.visible: false in fluxbox's init file.
The tools to be displayed are configured in the resource file, usually .fluxbox/init, with the entry toolbar.tools.
The toolbar width and transparency and layer can be configured via the toolbar menu. The toolbar menu is displayed if one right-clicks the clock or the workspacename in the toolbar.
The iconbar can be configured to display None, Icons from all workspaces, Workspace Icons, all windows from Workspace, All Windows from all workspaces.
How this is displayed is configured in the style file.