Basically, anywhere it is sensible to do so (ie where you cannot run aground, where there are no underwater obstructions or unless there are “private - no mooring” notices).  The Broads Authority does offer many free 24 hour moorings and you can moor at any affiliated Hoseasons boatyard free of charge, however, there are some moorings in private ownership which may charge a fee.  You can still find a public staithe in most villages.