The Crystal Cage (or 'Containment Crystal') is an artifact of witchcraft that can contain other magical beings or evil entities. In this case, it can be used to trap avatars behind a force field.
The forcefield is very simple and meant for roleplay/fun purposes only.
{primary} The 'Containment Crystal' is found by reading Chapter 2 after conjuring the Book of Shadows from your HUD. It comes with instructions on how to use it.
After rezzing the Crystla, simply type /5 trap AVATAR NAME to activate its magic on the target avatar. (Example: /5 trap torley )
Dispel the forcefield by typing /5 end