First, if you installed from RPM's all of that stuff should have been taken care of for you. Well, let me rephrase, the database and data directory should have been created. (It likes /var/pgsql/data). If you compiled it yourself please refer to the extremely detailed instructions in the INSTALL file that came with the source. FYI you need to specify the data directory with the -D switch
/usr/bin/postmaster -D /var/pgsql/data
There should also be some scripts put in the /etc/rc.d/init.d directory for PostgreSQL. You can use those as ROOT to start and stop the server.
If you want to accept connections from any machine other than the localhost you need to add -i switch to the startup.
/usr/bin/postmaster -i -D /var/pgsql/data
Your second problem will be solved when you actually get the postmaster running. It can't connect to a server that isn't actually running.
The pg_hba.conf is quite well documented right within the file. It has a number of examples as well. If you need any specific help then feel free to ask.
Tim Frank