Your Invoices and Quotes come with two options:

Item Invoices and Item Quotes, and

Service Invoices and Service Quotes

Item calculates the number of items x the price per item

     so 10 Apples at $1 equals $10,

     or 10 hours at $50 per hour equals $500

Service is merely a comprehensive description of what you are providing to your customer.

Choose the format that best suits your business and your style of operation.  For instance, Trades people could use either.  Businesses that sell "things" would use the Item Invoice.  Service businesses that require explanation of what was provided would use the Service Invoice.

Note that the Sales (Items) Report can only function from using Sales ITEM invoices.