Best thing is to read the manual. You didn't say which version of the tools you're using, but if in IC61X you can use cdnshelp to access the documentation, and then it's under Cadence Shared Tools/Virtuoso Hierarchy Editor User Guide. There's also some coverage in the Analog Design Environment/Virtuoso Analog Design Environment L User Guide.
These are in <ICinstDir>/doc/cdshiereditor/cdshiereditor.pdf and <ICinstDir>/doc/anasimhelp/anasimhelp.pdf (in IC5141 too).
Or you could take the radical step of using the Help menu in the hierarchy editor itself to access the documentation...