Might help to just start with a very simple empty share. Create users and groups (you’ll need to add them in TrueNAS UI). Try accessing the share from another computer on the network using the username/passwords you created.
Once you have multiple users set up and verify they can access the share at all, then try creating folders in the share and play with the permissions. Give a user or group access, make sure they are the only ones that can access it, and others are denied.
Might also help to find a video or tutorial on how permissions work for Linux.
If you run into a road block, just tell us what problem you’re running into.
Ignore quotas, scsi, and all the ancillary stuff for now and just focus on a share, users, permissions. Once you get the hang of permissions, the rest will be pretty easy.