remote access

Hi, I am trying to access a remote database using database link but I keep encountering hitting some error messages. I will be glad if someone could point out my mistakes or how to troubleshoot them.

What I did:

SQL> create database link dlink using 'billusr01/billusr01_at_powprodb';

note: powprodb is the SID of the remote database.

SQL> describe user_tables_at_dlink;
ERROR:
ORA-12154: TNS:could not resolve service name Received on Fri Nov 20 1998 - 01:11:31 CST