The File Manager tab, found on the right hand side of the screen, manages the list of files returned by your latest search.
When clicking on a row in the File Manager, it will expand the row and reveal further information about the file:
...
Furthermore you can activate the file which is currently expanded by clicking the Pin as active button: 
To change the active file just double click on the row/file you want to be active.
It includes three tabs: Management, Context and Layout.
The Management tab allows you to
import or export files
manage notes or attachments on selected files
print a set of filled forms for the selected files
delete selected file
set file status
renumber file
mark the selected file as first and second file in a file link operation
The Context tab allows you to
transfer a file to an agency
manage file restrictions
manage container links (e.g. link MPUB files to a Disaster Container)
Finally the Layout tab allows you to
print the list of search results
save the current grid layout
load a previously saved grid layout