To create an attribute, go to the Management tab and sub tab, Attributes.  Click the green plus sign seen in the tool bar.  Name the attribute and click Save.

Click the attribute you had created and select the plus sign to apply settings.  Name the element and choose the type.  Click Save. Next, apply the attribute a site.

Choose the site you want to apply the attribute to and then select the attributes tab.  Click the Assign button.

Choose the Attribute Set and click OK.

Click Edit and apply attribute selection. Click OK to complete.