Using EXPLAIN to obtain the execution plan

-- Estimate SQL Plan
EXPLAIN PLAN FOR SELECT * FROM tbl1;
SELECT * FROM TABLE (DBMS_XPLAN.DISPLAY);

-- set STATISTICS_LEVEL
ALTER SESSION SET STATISTICS_LEVEL = 'ALL';

-- Execute SQL
SELECT /*+ gather_plan_statistics */ * FROM tbl1;

-- checking previous SQL ID
set linesize 200
set pages 100
col SQL_TEXT for a100
SELECT s.prev_sql_id
     , sq.sql_text
  FROM v$session s
  JOIN v$sqlarea sq ON s.prev_sql_id = sq.sql_id
 WHERE s.sid = (SELECT sid FROM v$session WHERE audsid = USERENV('SESSIONID'));

-- Display Explain
SELECT * FROM TABLE(DBMS_XPLAN.DISPLAY_CURSOR(sql_id => '<SQL_ID>', format => 'ALLSTATS LAST'));