I. To Pin a Panel

The Contents, Bookmarks, Find and Replace, and Error List panels call be "pinned" to stay open. Alternatively, to free up screen space, they can be "unpinned" to display only when selected.

Either:

click the tab name of the panel you want to display

or
click the corresponding took name in the Searching or View groups on the Home ribbon tab

The panel opens.
Click the pin icon in the top, right-hand corner of hte panel. The panel is now pinned in place.

Tip: Clickin the pin icon again will hide the panel once you click elsewhere.