database link

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_remotedb';

note: remotedb the SID of the remote database.

SQL> describe user_tables_at_dlink;
ERROR:
ORA-12154: TNS:could not resolve service name Received on Mon Mar 22 1999 - 21:01:54 CST