Hi Debbie,
The capabilities afforded by Permissions granted in Moodle are dependent upon "context", and are mainly summative where many roles apply. The 'Authenticated User" is a role for everyone who is logged in. So if you're dealing with something on the Front Page the predominant role will be the Authenticated User. Note this can be set to any role you wish, but check Moodle Docs Front Page for more help.
In a Course, those enrolled will also have the Student role, so any hiding of a block will require you to delete permissions for the Block for both Authenticated User and Student roles.
You may wish to read through the Moodle Docs on Permissions, Roles, and Context, as it is a little confusing at first, but once you get it, you see how powerful it is.
As an aside, the permissions aren't always summative. A Role can "prohibit" a function / feature, which means that even if it is allowed in one role, setting the prohibit permission in another role will ensure it is not available. In that case, using prohibit on the Authenticated User role would stop anyone but a Site Administrator from accessing the feature, so be careful.
kind regards
Gary