Thank you for joining this thread, bmblebee.
I understand that you need to choose a category for the items you're selling. You can use Sales or Sale of Product Income depending on how you want to track what you sell.
You can use an income account QuickBooks already set up for you. But if you need a new account, scroll to the top of the drop-down list and select + Add new. Or learn more on Chart of Accounts first to help categorize your transactions.
Upon sharing this, I still suggest consulting your accountant to help you categorize your products. They can provide specific instructions to ensure your books have accurate records.
If you buy and sell many different things, you can use categories to easily find products or services. See the attached screenshot below as your visual guide.

If you want categories to show on forms like invoices and sales receipts, check out this article: Customize the forms you send to customers.
In addition to this, categories help you with reporting products and services. When you run sales or inventory reports, they're grouped in a way that makes sense to you.
Let me know if there's anything else you need. I'll be right here to answer your questions.