PostgreSQL server issue unix domain socket

PostgreSQL server issue unix domain socket

I followed these steps to install PostgreSQL with Homebrew (first time
using Homebrew):
http://dhilipsiva.blogspot.se/2013/02/install-postgresql-on-os-x-using.html
The last step didn't work. I assume it is supposed to start the server.
However, I think I successfully created a database cluster and started the
database server following the official documentation (17.2 and 17.3):
http://www.postgresql.org/docs/9.2/interactive/runtime.html
My problem is that when I try to create a database using createdb mydb in
the terminal, I get the message:
createdb: could not connect to database postgres: could not connect to
server: No such file or directory
Is the server running locally and accepting
connections on Unix domain socket "/var/pgsql_socket/.s.PGSQL.5432"?
I'm very confused since a lot of the concepts being thrown around here
(like sockets, path variables etc) are new to me. I'm also confused about
the directory structure in Mac OS X, since I recently migrated from
Windows. If anyone could just point me in the right direction it'd be much
appreciated.