So you need to have a dataset to store all of your plex files in like I do here:
You can see, I have the plexmediaserver_1 jail but I also have a dataset under my main volume called PlexMS to store my stuff, that should be your shared folder for media, videos, etc. Here is a picture of my plex plugin and the default jail location being provided:
No setup, simply default parameters for this one. I did that after creating the dataset not that it matters. Now, that will make the jail that you already have, now you have to go make a jail storage as you can see here and direct it to the dataset that was created in my case 'PlexMS':
that destination is the /media folder in the plexmediaserver_1 jail, that being said all the data automatically goes there and it protects you from messing up the jail itself. Now, go make sure you have a share setup to that dataset I used Windows SMB:
Those settings work 100% for me so far, when you access the share which will be the created dataset, all your movies can go right in it and they will be synced to the jails for plex, in turn giving you access to all your movies in the WebGUI. Follow these steps and it will work properly. If after all this you're still having issues this is where I learned to set it up:
How to Setup Plex Media Server on FreeNAS
Best of luck,
Vito Reiter
Quick Edit: Everywhere you see 'StoBro' for me is going to be 'HomeServer' for you. Make that the only difference.