My question is
1)Different header partners in VBRK table we could two partners SP,PY.
System takes Sold to party also into consideration?If so what about Bill to party
2)Different header fields-what are those fields?
For these sort of query, it would be better if you test in your system by changing the partner functions and see the end result so that you will learn something on your own which you never forget in your career. As for as possible, first try on your own, post here if you face any issue and we are here to help you out.
G. Lakshmipathi