How to see Explain Plan from SQL*Plus

Method 1: Autotrace Facility

When the AUTOTRACE setting of SQL*Plus is enabled, SQL*Plus will print an EXPLAIN PLAN and execution statistics after each SQL statement.
Here is an example, where AUTOT is abbreviation of AUTOTRACE

SQL>SET AUTOT ON
SQL>SELECT * FROM TEST WHERE A=1;

A B
---------- ----------
1 USA


Execution Plan
----------------------------------------------------------
Plan hash value: 2109870067

--------------------------------------------------------------------------------

| Id  | Operation                   | Name        | Rows  | Bytes | Cost (%CPU)|
Time     |

--------------------------------------------------------------------------------
|   0 | SELECT STATEMENT            |             |     1 |     8 |     1   (0)|
00:00:01 |

|   1 |  TABLE ACCESS BY INDEX ROWID| TEST        |     1 |     8 |     1   (0)|
00:00:01 |

|*  2 |   INDEX UNIQUE SCAN         | SYS_C005994 |     1 |       |     0   (0)|
00:00:01 |

-------------------------------------------------------------------------------


Predicate Information (identified by operation id):
---------------------------------------------------

2 - access("A"=1)


Statistics
----------------------------------------------------------
147  recursive calls
0  db block gets
26  consistent gets
6  physical reads
0  redo size
439  bytes sent via SQL*Net to client
458  bytes received via SQL*Net from client
1  SQL*Net roundtrips to/from client
0  sorts (memory)
0  sorts (disk)
1  rows processed

To trace the same statement without displaying the query data, enter:

SQL>SET AUTOTRACE TRACEONLY

To off trace issue,
SET AUTOT OFF
Method 2: DBMS_XPLAN Package

SQL>EXPLAIN PLAN FOR select * from test where a=1;
Explained.

SQL>set linesize 140
SQL>SELECT * FROM TABLE( dbms_xplan.display);

PLAN_TABLE_OUTPUT
-----------------------------------------------------------------------------
Plan hash value: 2109870067

----------------------------------------------------------------------------------------
| Id  | Operation                   | Name        | Rows  | Bytes | Cost (%CPU)| Time     |
----------------------------------------------------------------------------------------
|   0 | SELECT STATEMENT            |             |     1 |     8 |     1   (0)| 00:00:01 |
|   1 |  TABLE ACCESS BY INDEX ROWID| TEST        |     1 |     8 |     1   (0)| 00:00:01 |
|*  2 |   INDEX UNIQUE SCAN         | SYS_C005994 |     1 |       |     0   (0)| 00:00:01 |
-------------------------------------------------------------------------------------

Predicate Information (identified by operation id):

PLAN_TABLE_OUTPUT
-----------------------------------------------------

2 - access("A"=1)

14 rows selected.