Basically I'm a noob with database work and just need a kick start to complete the rest of my other diagrams, seeing as the use case was the first step I thought I would ask for some help

So this is my situation, can someone help me make a use case diagram for someone buying a book from me;

""I own a business which sells textbooks and other
educational books to students attending local secondary schools and tertiary institutions.

I currently sell these items using a small shop in town but have decided to move to an online presence only to reduce the cost to students.

Currently, my business has an established database for inventory items and a sales system to record the details for sales made. Both of these systems will continue to be used and I may make reasonable assumptions as to the type of data these systems contain.

The sales
system captures details of sales made and updates the inventory system for items sold. The inventory system contains data about individual stock items held including purchase and
sale prices, item description, and quantity on hand. There is currently no system to show details about who buys items because all sales are based on cash (cash, cheque, credit
card, eftpos) transactions.""