Login to PL/SQL Developer in Host DB where we want to create Database Link and execute below query to create:
CREATE PUBLIC DATABASE LINK ora_std_link CONNECT TO apps IDENTIFIED BY password USING '(DESCRIPTION= (ADDRESS=(PROTOCOL=tcp)(HOST=ora.oracle.com) (PORT=1521))(CONNECT_DATA= (SERVICE_NAME=ORACLE) (INSTANCE_NAME=ORACLEDEV)))';
Apps -> User name of Target/Remote Database
Password -> Password for above username of Target/Remote Database
In USING string give the Target/Remote instance tns entry from tnsentry.ora file in a single quote.
Run Query to check if DATABASE LINK was created:
select * from dba_db_links
Run below Query from the host Database where DB Link was created to check if it is working and able to connect to Target/Remote database:
select sysdate from dual@ora_std_link.us.oracle.com ;
Step-4: To Drop DATABASE LINK:
DROP PUBLIC DATABASE LINK "ora_std_link.us.oracle.com" ;
NOTE : Check in table -> user_sys_privs if you have all the PRIVILEGE to CREATE/DROP database link.