As shown in the image above, an attribute set can have only one attribute, by example Color or as many attributes as required, by example Size, Lot Number and Serial Number.
The way to get that is just to select the previously created attributes in this tab.
You should take into account that:
- if one of the selected attributes is a "Lot" or a "Serial N?" type attribute, the corresponding Number Sequence must have been properly setup in the Attribute Set window.