Documentation by Dysphunkional
To access your FreeNAS server with a SSH client like PuTTy you have to configure it and turn on the service.
Go to Services -> SSH.
Leave the TCP Port at the default of 22.
If you want to be able to login as root using a password check the Login as Root with password box. It is probably safer to add another user as a member of the wheel group. FreeBSD systems typically use toor (root backwards) for this type of thing.
The rest of the options can be left at their defaults.
Click the OK button to save your settings.
Start the SSH Service
Go to Services -> Control Services.
Click the off switch next to SSH to turn it on.