SQL> explain plan for
  2  select 1 from dual;

Explained.

SQL> select * from table(DBMS_XPLAN.Display);

PLAN_TABLE_OUTPUT
--------------------------------------------------------------------------------
Plan hash value: 1388734953

-----------------------------------------------------------------
| Id  | Operation        | Name | Rows  | Cost (%CPU)| Time     |
-----------------------------------------------------------------
|   0 | SELECT STATEMENT |      |     1 |     2   (0)| 00:00:01 |
|   1 |  FAST DUAL       |      |     1 |     2   (0)| 00:00:01 |
-----------------------------------------------------------------

8 rows selected.

SQL>