Audience Management is a very powerful feature that will enable you to sync and target any number of accounts and/or people on third party platforms. Because of that, you must have Admin level accessibility in order to use this feature.

If you do not have Admin level permissions, then you will not be able to access Audiences in Engage.

Note: Since this is an admin only feature, there is no concept of "Public" audiences. All admins will be able to access and manage all audiences.