Variant groups is an optional feature that allows you to regroup the different options available for your variants such as by color and size. See for more information. You must first enable the Product variant groups feature under Configuration > Products.
For example, the current iPad comes in Black or White and 16GB or 32GB. We would then create 2 variant groups name "Color" and "Storage" to store the relevant attributes. The attributes can be edited under the Option tab of each group.
Then edit their options,
Which will now make the variant groups accessible when creating possible combinations of variants
By selecting the proper variant groups in the dropdown menu.
Once you defined your variant groups, your individual variants can then be assigned to one of the available variant group combinations (Black 16GB, Black 32GB, White 16GB, White 32GB, etc.). Once all your variants are associated, the Product Detail module control will allow the customer to pick a variant using the variant groups Color and Storage.
Remember to associate every variant to one of the possible variant group combinations to make sure all your variants are reachable by your customer.
You can automatically show/hide optional groups depending on the previous selection. Suppose the Storage is only available in White color. In this case, you don't want to show the Storage choices unless the customer selected the White color. To make the Storage a conditional group, create a new option with an empty Name field. The empty name indicates to the system that this group has a condition.
Since the Black color iPad no longer offers choices for storage size, you would now associate it to the combination that does not specify a Storage option (i.e. Black color only without a Storage size).
The resulting list of variants look like this below. Notice, the Black only comes without any Storage choices.
The customer will no longer see the Storage choices if the Black color is selected. If the customer selected White, the Storage choices will then appear as usual.