Composite Item
You can designate an item as a composite item by editing the item (Inventory -> Items) and marking Yes for the Composite Item setting.
After saving the item with Composite Item set to Yes, you can click the Add/Edit Component button to add the sub-pieces to the composite item. You can also get to this edit tool by going to Inventory -> Home -> Manage Build Orders -> Edit BOM Definitions.
You can build composite items using the Inventory -> Home -> Manage Build Orders process.
You can set up the system so that composite/BOM items are created automatically during shipping by activating the BOM Auto-Create During Shipping add-on.
You can import composite/BOM definitions via a CSV file by activating the Import BOM Definitions and Build Orders add-on and going to Tools -> Import -> Import BOM Definitions.