Lookup from a Table

If you use dropdown box to select a category you don't need to do anything extra. Just make sure you select Category ID as a 'Link field' and Category Name as a 'Display field'.

I'am quite new to PHPRunner and I can't followup the above quote. I kindly want to know how to lookup from another table into my working table camp.
essample: I have a main table "TabEmployee" including a department as a combo camp and another table "TabDepartment" with "desc_department" and "cod_deparment" camps how can I lookup the "TabDepartment.desc_department" into "TabEmployee.department" through select from the TabDepartment.desc_department camp.

Please kindly help with a simple code.

Thanks.