You select which libraries are available to users when using this authoring portlet in the Library Selection section.
Libraries selected using the "configure" view are available on all instances of the authoring portlet, regardless of the page on which the portlet appears. Libraries selected with the "edit shared settings" view are only available for the current instance of an authoring portlet.
The libraries available in the "insert links" and "insert images" dialogues are based on the libraries selected in the "configure" view. If you select a library in the "edit shared settings" view that is not selected in the "configure" view, you are not able to select items from this library when using the "insert links" and "insert images" dialogues.
If you syndicate or import a library, it is not automatically added to the list of configured libraries for an authoring portlet on the target server. You need to add the syndicated or imported library to each authoring portlet on each server.