I suppose osx built-in installation may cause conflicts.
http://stackoverflow.com/questions/12472988/postgres-could-n...
postgres app fixed it
This is a consistent source of trouble when installing Postgres. Usually, this involves looking up the right places to modify the path and sometimes needing to change permissions/ports.
While it is really easy to install most of the time, I'd say the Postgres.app works well for people who aren't developers but need to use PostgreSQL.
initdb /usr/local/var/postgres -E utf8
Also if you are working with rails, add host: localhost in your database.yml file and remove the user password. That should be all you need.
This is probably "elitist" of me but I feel like someone who isn't comfortable with the command line should be learning that before they tackle Postgres.