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 Creative Workflow preset, 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 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.
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.
Read more about managing permissions in Permission Management here.