can't connect to server

I have just started using Django with Postgres 9.0.

Actually, the first time I set up my database with Django it worked fine.
However, I just created a second Django project with a new database and
connection to Postgres (everything has been single user databases on the
localhost). After creating my first tables, when I try to get into the
Postgres shell from the command line I receive the message:

'Could not connect to server: Connection refused
is the server running on "localhost" and accepting TCP/IP connections on
Port 5432?'

I've looked through a number of articles on how to address this problem.
However, I'm obviously not understanding some very basic information.

1. If I want to run 'postmaster' from the command line, what does my
directory need to be? Where does the executable file reside within
...Postresql/9.0? Every directory I've given the command to tells me it is
not an internal or external command.

2. Where does my database data reside? I have no good idea where data goes
when I create a database or what kind of files I should be looking for.

3. I never changed anything in my postgres.conf or pg_hba.conf files? Is
there anything I should look for in those files that might prevent the
server from running or accepting any connections?

Thanks much,
Eric