Sizo,
You need to populate the WorkCentre field in your complex table by adding code to the java or database script that populates this table. Just adding the field and index wont accomplish anything if you don't populate the field from code. Seems like you are kind of flying blind here on some basic concepts. I would suggest starting on the Agentry landing page here:
http://scn.sap.com/docs/DOC-47882
There are tutorials here that explain how to do things from scratch. You could also take a class on Agentry development. Get familiar with how things work, then come back with specific questions. At this point, it seems you are somewhat lost on the basics.
Jason Latko - Senior Product Developer at SAP