The attribute sets are libraries of reusable attributes. In the templates section of the administration, click the Attribute sets tab to manage the set of attributes. The attributes defined here can then be used in different templates.
To add a new set, you have to click on the Add attribute set button and then it is sufficient to specify a unique name. Moreover, you can select an existing set to see all the associated attribute definitions.
In the right side of the Properties panel you can define a new attribute by filling the Attribute name and clicking on Add/Update, the new attribute will appear in the Attributes list. You can reorder the position of the elements in the list and of course you can select whatever attribute and modify it's definition at any time.
For the attributes of type String you can also define the Input Mode preset that will display to the end user a list of possible options to choose. The options can be managed by clicking on Attribute options.
You can also Import and Export huge lists of options in CSV format.