Permissions manage what users can do in their portal. For example, you can manage who can view or create collections, download specific assets, see the statistics for the portal, manage the look and feel of the portal, add stages to workfow, or remove versions of assets.
Permissions are closely tied with users and user profiles. Users must be assigned to a user profile, and a user profile must have specific rights defined. You can add and remove rights from the profiles as necessary.
You need to have the Permission management right to add and remove permissions for user profiles. It's advisable that only a heavy user, such as the administrator, manages permissions for users.
Go to Settings > Users & rights > Permission Management to manage permissions for the portal.
Make sure you have all the permissions under Brand selected for all user profiles. Otherwise users won't see any assets at all.
You can also manage permissions on the metaproperty options level. For example, you might decide to hide assets tagged with a selected metaproperty option for some users or user groups. You can also decide to hide assets linked to that metaproperty option but show them to selected people.
To add more granularity to permission management, you can also set permissions on the asset level. Granular permissions take precedence over the generic ones, so when you hide an asset from users on the asset level, it will remain hidden even though these users might have full view rights in their permission profile and on the metaproperty option level. See Manage permissions on the asset level.