sales order header functionality

hI,

i WANT TO KNOW THE FUNCTIONALTY OF SALES HEADER.

lIKE WHEN I SELECT SELL-TO-CUTOMER THE CUSTOMER ADDRESS CITY POST CODES ARE GETTING UPDATED.

HOW TO SET THESE RELATIONSHIPS AND HOW IT IS FUNCTIONING EXACTLY GIVE ME A CLUE

you need to read all the resource you have, go to the basic, check the Help file.