The tool bar is a container control that is placed on top of many windows. It is mostly used to provide access to commands that apply to the whole window.
If the toolbar includes more controls that can be shown due to the limited window width the hidden toolbar controls can be selected by clicking on the drop down arrow at the right border of the toolbar (figure 1: 1)
The controls shown on the toolbar may change depending on the current context. E.g. if the window has a tabs controls that refer to a specific tab will be shown only when that tab is active.
Figure 1: The toolbar of the view explorer window