This tab is available only if it has been enabled with the Show Table/Column Privileges checkbox in the Administrator section of the Options dialog. 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.