Hello Hamed,
Sales is the only transaction when money change hands and you can not go back and make changes to that sales receipt (Quote, Work Order and Layaway) are the process towards Sales
A sales quote is a generated price list of items to sell. When creating a quote, no
money is exchanged, and items are not committed. If the customer decides to
purchase the items from the sales quote, it can be converted to a sales invoice or
a Work Order.
A work order is a saved transaction that can be retrieved later, and usually
involves some form of service, repair, or customization. A deposit for the items is
usually taken and is defined within Manager Configuration. For example, for a
computer store that builds its own computers, the user can create a work order
listing all of the parts for the computer, and then turn the work order into a sales
invoice when the work is completed.
A layaway is a process where a customer pays in increments and receives the
item when the item is fully paid for. The customer must place a minimum deposit
that is defined with Manager.
Backorder, If entering an item that does not have the available quantity on hand to meet the desired quantity at the POS, Store Operations opens the Insufficient Quantity
window; select from the following:
• Back Order − Enables the cashier to generate a back order. (take order in advance and ask your supplier to ship, same way like PO works)
• Accept Requested − Allows the cashier to sell the quantity requested by the customer.
• List Substitutes − Enables the cashier to suggest an alternate item.
• Cancel − Returns the cashier to the previous step.
I hope this will help you understand, best way to understand is, to do it practically and see how it works
