Oracle database, how to create new instances by command

Hello there!

For your reference, more support from Oracle is needed:

[root@centoscms ~]# su - oracle

[oracle@centoscms oradata]$ ORACLE_SID=mydb
[oracle@centoscms oradata]$ export ORACLE_SID
[oracle@centoscms oradata]$ echo $ORACLE_SID

[oracle@centoscms oradata]$ mydb

[oracle@centoscms oradata]$ mkdir -p $ORACLE_BASE/admin/mydb/adump;mkdir -p $ORACLE_BASE/admin/mydb/bdump;
[oracle@centoscms oradata]$ mkdir -p $ORACLE_BASE/admin/mydb/cdump;mkdir -p $ORACLE_BASE/admin/mydb/udump;
[oracle@centoscms oradata]$ mkdir -p $ORACLE_BASE/admin/mydb/pfile;mkdir -p $ORACLE_BASE/oradata/mydb;