when I open the SQL command lineHow? Did you provide userid/password? Initially you should see something like (important is 'connected to')
You get what you ask for, not what you want. A connection to the database requires ... connecting.Same problem. No solved.
$ sqlplus /nolog connect system ... password ... Connected. create user <username> identified by <password> [ default tablespace users]; grant create session, resource to <username>; connect <username> ... Password ... Connected.