You can use Kits/Bundles to complete a few different objectives:
1. You can create a Kit to wrap a SKU as another SKU. This is common when you sell 1 item on Amazon under a few different ASINS.
2. You can create a Kit to sell 1 item as a 3 pack. To do this create a kit with the single item within it and set the kit quantity for that line item to be 3.
3. You can create a Kit to group single items together under 1 SKU which is commonly called a 'bundle'. In this case you have a number of individual items that you sell separately but want to also sell as a group.