I have a requirement from the client 
The form contains the field purchase order number,order name, vendor account 
If I choose the purchase order from the lookup the fields nearby in the form must display the corresponding field records in the lookup of  two field in that I have to select the record and insert it

The another process is if I choose the vendor account in the form means the remaining fields order name and the purchase order number must display the lookup for the related vendor field data's in their lookup