A bill records what you owe your vendor. It is Brahmin Solutions' copy of the invoice they sent you.
How it relates to the order
A bill belongs to a purchase order. One order can have several bills — useful when a vendor invoices each delivery separately, or splits an invoice across months.
Purchase order → Bill 1 (first delivery)
→ Bill 2 (the rest)
Together the bills should add up to the order. Brahmin Solutions will not let you bill more than was ordered.
Bills and receipts are independent
This trips people up. A bill and a receipt are both linked to the purchase order, but not to each other:
You can receive stock before the invoice arrives
You can enter the invoice before the stock turns up
Deleting a receipt does not touch the bill, and vice versa
The purchase order is what ties them together.
What a bill does not do
A bill does not add stock. Only receiving does that. If you enter a bill and your stock count has not changed, that is correct — you have recorded what you owe, not what arrived.