Virtual box has this little secret, the Command Line interface (CLI), this is very useful for users who wants to manage their virtual boxes on headless servers.
Question is why using command line while you have a nice easy to use GUI, the answer is POWER. you can do anything with the virtual box command line, you can create virtual machines, modify their settings, take snapshots, start and shutdown them.
VBoxManage supports everything the graphical user interface does, and much more.
VBoxManage has its share of Virtual Box documentation, you can find it here http://www.virtualbox.org/manual/ch08.html