I have the same question.  This is helpful.  To clarify, I have some examples:

I have a subcontractor who I paid for electrical work on a project.  I assume that would be a Category Detail, right?

I buy material for a job that is COGS, each line item on that material receipt would be an Item Detail, right?

Those materials should be added to my "Products/Services" list.  When setting that up, that's where I would code things to be COGS.  But what about things that are not COGS that I buy and use in business.  That could be paper clips or it could be gas in the truck.  How would I create expenses for both of those items?

Should everything I buy in my business be listed under Products?