How can I make a report to show me how many of each product was sold ?

You can pull up the Sales by Product/Service Detail or the Sales by Product/Service Summary report to achieve your goal, Malcolm. I'll share the steps below.
 

If you want a detailed product/service report that shows an item's quantity per sale along with its complete information in a given period, run the Sales by Product/Service Detail:

1. Go to Reports, then Standard reports.
2. Scroll down to the Sales and customers section.
3. Select the Sales by Product/Service Detail report from the list.
   
4. Modify the Report period accordingly. If you're on the Classic view interface, click Run report to update the report's data.
   
   

However, if you prefer to have summarised data of your sold products, pull up the Sales by Product/Service Summary report instead. Just select the Sales by Product/Service Summary report from the Standard Reports page. Then, modify its Report period.

You may also add or edit the data on both reports to accomplish more sufficient results. The steps for this action vary for both the old and the new reporting interface. For complete guidance, check out these links:

• Customise report - Modern View
• Customise report - Classic View

Choose the report that suits you best. If you have more questions about tracking your items and their quantity per sale, feel free to circle back to this thread. The Community always has your back.