installing postgre

I began with a laptop, installed Red Hat Enterprise Linux 3. I do not know
what is included or not on this version. I downloaded some RPMs from
RedHat.com and used tech support to install all of them. I do not know what
all the RPM does, whether it goes to completion or just unzips some
compressed files. I found a book about PostgreSQL for a previous version and
used it. After using Red Hat technical support I used the book. I modified
the bash_profile for user account postgres, and my personal user account
according to instructions in the book. I get error messages concerning these
files.

I am kind of lost about PostgreSQL but if you will help me I will
persevere.

I have some error messages when trying to create a database using the
command: createdb "mydb".

Error message for both of those commands:

psql: could not connect to server: No such file or directory Is the server
running locally and accepting connections on Unix domain socket
"tmp.PGSQL.5432"?
createuser: creation of user "username" failed.

Or if I am trying to create a database I get the error message similar to
above but last line says: createdb: database creation failed.

I have created a user account called postgre, without the s on the end. I
do not know what ramifications this has.

I noticed after mistyping "postgre" that the username "postgres" was already
created.

The version I have installed in 7.3.

Thank you for helping me. Please email me and tell me what I need to do to
get it running.

Lee