1) Go to Products & Services -> Items to create a product or service.
2) Click the New Item button at the top right. This will open a modal, where you can enter all your product or service details.
Select item in an invoice
After you've created your product or service, you're able to add it to your invoice.
Simply type @ within the item column in an invoice to search for your item.
All data like the item description, price and account will be pre-filled based on your product item.