The status bar displays some helpful information about each selected command. For more information, the help icon in the status bar links to the documentation page corresponding to the command.
It is useful for checking that Hook is linking the correct context if e.g. a different document is frontmost than the the one you meant to link with, the status bar will show the title of a different document than you expect.
You can show or hide the status bar by using the ⌘/ keyboard shortcut. (The same hotkey as Finder uses to hide and show its status bar.) You can also show or hide the status bar by selecting “Show/hide status bar” in the Gear Menu.