Oracle Forms

Hi, ( I am working on forms 10 G )
I have to populate a combo box based on values from a table.
please guide me the procedure to do this ??

1) i have created a list item and changed property of of list item combo box
are any other properties to be changed ?

2) Now how will we dynamically create the record group and how to populate the
combo box ?

3) Which Trigger will we use ?

this is very urgent,
i will really appreciate ur time ..

Regards.