After clicking on the add button you will be prompted for a name and ID for your new permission set:
PLACEHOLDER - SCREENSHOT
The ID is automatically generated based on the permission set name, but you can change it if you wish. This ID will appear in data downloads, the audit report and can also be used in bulk uploads. Permission set IDs cannot be modified.
The Attributes tab gives you control over the PLACEHOLDER - SHIBBOLETH / FEDERATION STUFF
SHIBBOSTUFF BITS for FEDERATIONS
At the top right there is a display of the number of connected accounts and resources. Buttons beside the numbers let you modify which accounts and resources are associated with that permission set.
Modifying the permission set allocation
Modifying the resource allocation