When creating an item, what does the "Fixed" vs "Variable" pricing mean?

Fixed is the default. It means there's a set price that rings up at the register. Variable, when selected if you select or scan that SKU at checkout, Square will prompt you to enter a price.

Click "pricing type" in Rose inventory or take-in screen to select variable.

To sync the item to Square, you still need to add a price to save but you will be prompted for a price on Square when the barcode is scanned or you select the item out of inventory.

You'll also want to make sure "never deletes" is checked in Rose so that you can reuse the item until you decide to delete it from inventory.