PostgreSQL's access control mechanism is based on roles, objects, and privileges, allowing users to be granted specific permissions to perform actions on databases, tables, and other objects. Roles can inherit privileges from parent roles, but inheritance only occurs between roles, not between objects. Object owners have unique privileges that cannot be inherited by other roles. PostgreSQL provides default privileges for new objects created in the future, which can be customized using the `ALTER DEFAULT PRIVILEGES` command. To view current access control lists (ACLs), users can use psql CLI commands or query internal PostgreSQL tables. Understanding these concepts and configuring access control properly is essential to ensure secure and efficient management of database resources.