don't get me stupid but I have some little password problem

Dear Sirs,

I may be a taken a new Linux user and had installed Redhat 6.1 which also
includes your product.
I installed started the services and wanted to connect to postgresql using
psql as root but i couldn't.
it says

[root@tatooine emrah]# psql
Connection to database 'root' failed.
FATAL 1:  Database root does not exist in pg_database

i was using at my job MS SQL Server 7 an we had an "sa" user which was a
super user, who can create databases, tables, etc...

i searched your site and downloaded pdf book but the book at the beginning
"assumes" that i am a registered user.

Would you please help me to connect to postgresql so i can create databases,
tables, users,...
I think there has to be predefined user for this.I know it sound comic, but
I couldn't find an username and password anywhere...

Best Regards,
Emrah Benligil
emrah@netone.com.tr