This tab is available only if the Show Schema Object Privileges checkbox in the Administrator section of the Options dialog has been checked. It allows you to grant privileges on a table level or on a column level.
To access the tables, double click on the schema (database) name containing that table. You will not see and cannot grant privileges on a schema level in this tab; if you want to do that, use the Global Privileges tab instead. Also, you cannot select more than one table at a time.
If you want to grant privileges on a column level, double click on the table name; this will give you access to its columns. You cannot select more than one column at a time.
Privileges not assigned to the user are listed under Available Privileges. You can remove privileges by selecting them in the left box, and then clicking the > button. Removed privileges will appear in the Available Privileges box. You can assign privileges by selecting them in the Available Privileges box, and then clicking the < button.