The SELECT clause specifies three columns for the output. The prefixes on DEST are table aliases to specify which table to take the values of Dest from. The CASE expression creates a column that contains the character string to and from. 
   title 'All Possible Connections';
   select f1.Dest, case
                      when f1.dest ne ' ' then 'to and from'
                   end,
          f2.Dest