The Possible duplicate people tool uses the potential duplicates that you found with the Find duplicate people tool and lets you act on those records.
Use the Filters panel on the left and Apply filters button to limit which potential duplicates are shown. Note that duplicates which have already been combined/merged together do not show here, nor do potential duplicates which were found in the past but refer to one or more people who do not exist anymore (usually a result of combining people together).
Hover your mouse over a record to get a popup hint with details about both the source and target people.
Right-click on a record to:
Changes made here - other than combining people together - are not saved until you click Save.