How to perform undo operation using Oracle Basic Command

I am new with Oracle Database and I want to know some command relate with Oracle. Does anyone help me with below questions:

1. Which command use to show undo_retention period?
2. Which command use to show undo tablespace name?
3. how to disable/enable undo Retention guarantee?

Thanks,

1. Which command use to show undo_retention period?
2. Which command use to show undo tablespace name?

Open SQL*PLUS as SYSDBA and use show parameter command as shown below.

SQL> show parameter undo
NAME                                 TYPE        VALUE
------------------------------------ ----------- ------------------------------
undo_management                      string      AUTO
undo_retention                       integer     2400
undo_tablespace                      string      UNDOTBS1

3. how to disable/enable undo Retention guarantee?

Now you have the name of the undo tablespace.

Use the following command to switch to undo retention guarantee.

ALTER TABLESPACE UNDOTBS1 RETENTION GUARANTEE; 

To switch back to noguarantee.

ALTER TABLESPACE UNDOTBS1 RETENTION NOGUARANTEE; 

Use following query to check whether your undo tablespace has retention guaranteed or not.

SQL> SELECT tablespace_name, retention FROM dba_tablespaces where tablespace_name = 'UNDOTBS1';

For more details: Managing Undo