explain script in oracle 10g

SET PAGESIZE 100
SET LINESIZE 200
SET VERIFY OFF

COLUMN plan             FORMAT A50
COLUMN object_name      FORMAT A30
COLUMN object_type      FORMAT A15
COLUMN bytes            FORMAT 9999999999
COLUMN cost             FORMAT 9999999
COLUMN partition_start  FORMAT A20
COLUMN partition_stop   FORMAT A20

SELECT LPAD(' ', 2 * (level - 1)) ||
       DECODE (level,1,NULL,level-1 || '.' || pt.position || ' ') ||
       INITCAP(pt.operation) ||
       DECODE(pt.options,NULL,'',' (' || INITCAP(pt.options) || ')') plan,
       pt.object_name,
       pt.object_type,
       pt.bytes,
       pt.cost,
       pt.partition_start,
       pt.partition_stop
FROM   plan_table pt
START WITH pt.id = 0
  AND pt.statement_id = '&1'