The Accounts tab has two sub-tabs:
Server Access Management
Schema Privileges
Server Access Management allows you to list existing user accounts. You can also add and delete accounts. You can allocate administrative roles and also set account limits.
Schema Privileges allows you to set specific privileges on a user basis.
In the current version of MySQL Workbench it is not possible to manage privileges below the schema level. For example, it is not possible to view or manage grants at the table, column, or procedure level. Support for this feature is however planned for MySQL Workbench 6.0.