New Permission Scope can be added by clicking on Add button above the list. This button changes due to selected Permission Scope Type in the left panel. If e.g. Organization is selected, than text on button is Add Organization, and the form to create a new Organization will be open. If you have not selected any Permission Scope Type (Everybody or Users is selected) you first have to select Permission Scope Type in a popup.
After selecting Permission Scope Type, a form containing properties for the type will be opened. At least all mandatory fields must be defined.
Same form is shown when you edit Permission Scope.