Open Command Line Interface Window as a Administrator, now issue command sqlplus

Note**: As Administrator set the container from CDB$ROOT to pluggable database (orclpdb)
C:\Users\devi>sqlplus

SQL*Plus: Release 12.2.0.1.0 Production on Wed Mar 30 21:56:44 2022

Copyright (c) 1982, 2016, Oracle.  All rights reserved.

Enter user-name: sys as sysdba
password:******

Note**: As Administrator Set database to pluggable database;
SQL> alter session set container=orclpdb;

Session altered.

Note**: As admin change con_name mode from MOUNTED to READ/WRITE if not already;
SQL> alter pluggable database open;

Pluggable database altered.

Note**: Now Login to hr to work with
SQL> conn hr/hr@ORCLPDB
Connected.
SQL>exit;

Enter user-name: hr@orclpdb
Enter password:  hr
Last Successful login time: Wed Mar 30 2022 23:34:03 +06:00
Connected to:
Oracle Database 12c Enterprise Edition Release 12.2.0.1.0 - 64bit Production

SQL> select * from departments;

DEPARTMENT_ID DEPARTMENT_NAME                MANAGER_ID LOCATION_ID
------------- ------------------------------ ---------- -----------
           10 Administration                        200        1700
           20 Marketing                             201        1800
           30 Purchasing                            114        1700