I decided to create a separate section for Jails. I did this so others can easily add their plugin guides after this one. In this way a repository of different plugins can be accumulated over time.
The user of this guide can then choose the one they need for the plugin of their choice.
Jails basically allow the FreeNAS OS to be customised in particular ways to provide extra functionality and offer additional services that did not come with the standard FreeNAS OS.
Jails also provide another very important function in addition to this. If any program running in a Jail hangs, crashes or falls over (like Fester when he has had one sherbet too many) the Jail acts as a bulwark so the FreeNAS OS and other Jails do not also crash.
Jails also supply a totally independent network stack which can be very useful and ensures a certain amount of resilience when things go wrong.
Before we get to the specifics of configuring a particular plugin we first must set the conditions within which all the Jails will operate.