starting up database server + user postgres

Hi,

I'm a novice for using Postgres and Linux - any help or suggestions would be really appreciated, thanks!!!  I'm having
troublelogging on as the postgres user.  I wanted to 
create a database, so I tried...

root# /usr/local/pgsql/bin/createdb test
psql: could not connect to server: No such file or directory
        Is the server running locally and accepting
        connections on Unix domain socket "/tmp/.s.PGSQL.5432"?
createdb: database creation failed

(so i thought i probably needed to logon as postgres, so i tried...)
root# su - postgres
su: user postgres does not exist

root# adduser postgres
adduser: group postgres exists - if you want to add this user to that group, use -g.

root# chown postgres /usr/local/pgsql/data
chown: `postgres': invalid user


I'm a little stuck....can anybody help?  thanks so much!

jenn.