The districts list can be filtered for a few different reasons. One is to narrow down the list by criteria to find specific records. Another is to give you a count of districts, based on your selected criteria. 

As an example, if you wanted to know how many organizations districts have the same leaderyou could select a "District Leader" from the District Leader drop-down list. Click the "Filter List" button. You will see the total records label above the list has changed and gives you a total count of all districts filtered by the district leader you choose. The list has also changed, and displays only those districts that are lead by the leader you choose.

To get started, select My Organization > Districts - from the main menu on the left hand side.

To filter your districts, you must choose a district leader.  Click the "Lookup" button to search for and select the leader you wish to view districts by.  Then click the "Filter List" button.
Districts can only be filtered by their District Leader.  Once a leader is selected and the list is filtered, the list will display only the districts that have the selected district leader.