How to fetch particular value when i select some field in a Lookup ?

My web part is nothing but containing a AxForm in which i added 2 fields( OrgID,OrgDesc) into AxGroup.

I created a custom lookup in OrgID Axbound field.

OrgId 50 and it’s OrgDesc is Mumbai

So when i am selecting 50 from Lookup then OrgDesc field must show Mumbai.

I can’t understand where to do code ?

Whatever the fields are added into AxGroup are like combobox type or bound fields.

So how can i know control’s value in Enterprise Portal .