How to access user Created by OS externally

I am able to

SQL> create user ops$deskuser identified externally;

while deskuser is one of my OS user.

I believe it is a very easy question, however I just do not know how to access this user from sqlplus., please help

Thanks in advance

as long as you are logged in and deskuser from os level you can simply issue command:

sqlplus /

that should connect you to database with ops$deskuser.