Hello DeeCh!
Welcome, and thank you for asking for insight about assembly and group items. I'm happy to share information with you.
Inventory assembly is a group of items to be assembled, manufactured, or built before they are sold. It specifies the bill of materials (inventory parts and quantities).
Building assemblies is simply the process of entering the assembled quantities. Or, shall we say, it's recording how many quantities are already manufactured. This step increases the TOTAL QUANTITY ON HAND of a particular assembly item in the Item list window.
A group item, on the other hand, is just a set of combined items to be sold, so only one item name that represents them all will appear on the customer's invoice, sales receipt, or estimate. This doesn't require to be assembled, and you can still change the quantity of each item as you create sales transactions.
There you have it. If you need some more clarifications, just comment below. We'll be happy to help you again. Take care!