How to create the PLUSTRACE role in order to use the AUTOTRACE feature in sqlplus

Create the PLAN_TABLE in the schema you want to use it for (in this example, SCOTT):

CONNECT SCOTT 
@$ORACLE_HOME/rdbms/admin/utlxplan.sql 

Create the PLUSTRACE role:

CONNECT / AS SYSDBA 
@$ORACLE_HOME/sqlplus/admin/plustrce.sql 

Grant the PLUSTRACE role to SCOTT:

CONNECT / AS SYSDBA 
grant plustrace to scott;

You are now able to use the autotrace feature of sqlplus for user SCOTT.

Source: Oracle Documentation