postgres installed via rpms -can't run postmaster or postgres

Hi, I am relatively new to Linux and just installed postgres via rpms.
I think.  However, I can't for the life of me figure out how to start up
postmaster or psql.

psql - I keep getting the following error when running psql...

"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.1234"?"

How do I find out if the server is running locally and accepting
connections on Unix domain socket?

postmaster - I keep getting the following error when trying to start
postmaster...

"postmaster does not know where to find the database system data.
You must specify the directory that contains the database system
either by specifying the -D invocation option or by setting the
PGDATA environment variable."

Okay, set it to what?  man and postgres docs are of little help.  Any
help is much appreciated.  Following are the rpm's I ran
redhat-install-packages on.  I got them from a mirror off
postgresQl.org...

ostgresql-7.3-2PGDG.i386.rpm
postgresql-python-7.3-2PGDG.i386.rpm
postgresql-contrib-7.3-2PGDG.i386.rpm
postgresql-server-7.3-2PGDG.i386.rpm
postgresql-devel-7.3-2PGDG.i386.rpm
postgresql-docs-7.3-2PGDG.i386.rpm
postgresql-jdbc-7.3-2PGDG.i386.rpm
postgresql-libs-7.3-2PGDG.i386.rpm
postgresql-pl-7.3-2PGDG.i386.rpm

Oh, and another thing I'm confused about is...  I tried to install these
in /usr/local/bin, that's where the rpms are, but they wound up in
/usr/lib.  Any idea why that might be?  I rpm'd from /usr/local/bin

many thx
Eric