Newbie problem

Hello everybody:
  i can´t work with my Postgresql installation ( under Linux ), here
are my steps:

[shell]# mkdir /usr/local/pgsql/data
[shell]# chown postgres /usr/local/pgsql/data

[shell]# su - postgres
[shell]$ /usr/local/pgsql/bin/initdb -D /usr/local/pgsql/data
and then

[shell]$ /usr/local/pgsql/bin/postmaster -D /usr/local/pgsql/data

OK? well... if i try

template1=# createuser "check";

ERROR:  parser: parse error at or near "createuser"
ERROR:  parser: parse error at or near "createuser"

what is the problem??? thank you very much!!!