Panes can be pinned to a specific place or hidden when not in use. If you want to always see a window, pin it. To pin it, click the Auto Hide button in the title bar:
To hide a pane when it is not in use, click the Auto Hide button. When a pane is not pinned, the pane will be hidden when not in use. In order to access a hidden pane, hover over the tab that corresponds to the appropriate pane. The tab label corresponds to the title displayed in the pane's title bar.
The following is any example of a hidden pane: