Storage -> Pools shows you your datasets.
You have mounted media into Plex, the assumption is that this was a dataset. It could also be a folder.
Best practice is to use a dataset, as that allows you to easily set permissions. If it's a folder in your main pool, DO NOT set permissions recursively in the pool, you'll break things.
Scenario 1: You have a dataset for your media, and it's mounted in Plex. Set permissions on that dataset. Recursively is fine, assuming that the dataset is exclusively for Plex media, not for other things.
Scenario 2: You use a folder in the main pool (or inside another non-Plex dataset) for your media, and it's mounted in Plex. Or, you have a dataset, but it also contains child datasets that are unrelated. If that's so, you'll want to do some "untangling" so you don't have to try and massage permissions manually on command line. Create a dataset for Plex media, and only for that (Movies, TV and Music can live in folders inside that dataset), move all your media in there, mount it in the Plex jail, and set permissions on it.
There are videos and instructions that go into more detail on how to accomplish those tasks, including on my own YouTube channel. Find a format that works for your learning style.
Edit: For what it is worth, I disagree with user plex group wheel, it works but is brittle: Create a new folder in Windows, say for a movie, and access isn't granted because the user doesn't match. My preferred method for handling Plex permissions on a media dataset shared via SMB is documented yonder. It's not the only way, and I don't know enough to claim whether it's better than other ways. It does work.
https://www.youtube.com/watch?v=9Xsgsap0wgQ
Good luck!