virtualbox.org

What I do when I have questions myself, is to open the searchable PDF version of the User Manual. You should have a searchable PDF included with your installation (/opt/VirtualBox/UserManual.pdf). If not, there's the on-line manual in PDF format, again searchable. Take advantage of that fact, and use it to search the PDF for the terms that interest you.

For example, searching for "symlink" lead me to the chapter "Shared Folders" which contains some information that you might find useful...