Here is a great link from seller central which goes over adding variations: https://sellercentral.amazon.com/help/hub/reference/202135320
It is important to keep in mind that a variation may not always sell as quickly as the other variations. It could be something that people may not be interested in buying a multi pack of.
For example, there have been products where the single version of the product may sell hundreds or thousands a month, and the 2-pack variation may sell just a handful. It is important to stay on the safe side, as it can be risky since we have no historical information or trends about that variation. You should not go in with too much inventory in case the listing does not get any traction.
How do I create a product variation?
How will I know if a new variation will sell?