What is the Adaptive SQL Plan Management introduced in Oracle 12c?

By "Adaptive SQL Plan Management", Oracle is referring to a new autotask that is executed every night during the maintenance window, as a part of the "sql tuning advisor".

It will automatically evolve all non-accepted plans in the SQL Plan Management Base.
If the New plans improves the performance of the Query, they will automatically be promoted to an accepted plan.

In previous versions of Oracle, plans needed to be evolved manually by the DBA by running dbms_spm.evolve_sql_plan_baselines.

Is the sql tuning task enabled?

SELECT CLIENT_NAME, STATUS
FROM   DBA_AUTOTASK_CLIENT
WHERE  CLIENT_NAME = 'sql tuning advisor';

View details about a specific run:

SELECT OWNER,TASK_ID, TASK_NAME,DESCRIPTION,ADVISOR_NAME,EXECUTION_TYPE,STATUS,RECOMMENDATION_COUNT "num rec",EXECUTION_START,EXECUTION_END,LAST_EXECUTION,HOW_CREATED
FROM  DBA_ADVISOR_TASKS 
WHERE TASK_NAME = 'SYS_AUTO_SPM_EVOLVE_TASK';

OWNER	TASK_ID	TASK_NAME	DESCRIPTION	ADVISOR_NAME	EXECUTION_TYPE	STATUS	num rec	EXECUTION_START	EXECUTION_END	LAST_EXECUTION	HOW_CREATED
SYS	2	SYS_AUTO_SPM_EVOLVE_TASK	Automatic SPM Evolve Task	SPM Evolve Advisor	SPM EVOLVE	COMPLETED	0	13.11.2017 23:00:06	13.11.2017 23:00:07	EXEC_20606	AUTO

If the parameter accepted_plans is set to TRUE, it means plans will be automatically evolved:

SELECT PARAMETER_NAME,PARAMETER_VALUE
FROM DBA_ADVISOR_PARAMETERS 
WHERE TASK_NAME LIKE 'SYS_AUTO_SPM_EVOLVE_TASK'
AND PARAMETER_NAME='ACCEPT_PLANS';

PARAMETER_NAME	PARAMETER_VALUE
ACCEPT_PLANS	TRUE

If you want to view the results of such an automatic job, use the following code:

SET LONG 1000000 PAGESIZE 1000 LONGCHUNKSIZE 100 LINESIZE 100
SELECT DBMS_SPM.report_evolve_task(task_name => 'SYS_AUTO_SPM_EVOLVE_TASK', execution_name => 'EXEC_20606') AS output
FROM dual;