from the scenario write the function and non function

i want it on 22\12

the customer access the system through their account details, the customer type in search criteria to look for a specific products and when they see products they select them and they add them to their cart obviously. once they have got a few items, the next step there is a payment request to their bank and essentially the bank will then give them an approval. they will pay for the customer products provided they have got the money to pay for them otherwise they will be declined. the customer will get a receipt of the transaction these products will then be packaged by online shop sent to the customer door. the products are decreasing in quantity online shop, then need to purchase more products so essentially, the online shopping system need to contact suppliers and create a purchase order saying we need amount of new products to restock in order to keep able . customer buying these products so a purchase order is sent to the supplier. the supplier will give an pay invoice. Online shop needs to contact their bank, their payment request is sent for the purchase order product. the bank will give their confirmation and payment for the ordered items