Problem of installation on Mac

Hi, I am a newbie for pgsql and tried to install it on my MacBookPro
Intel. I got everything correct until creating the user: postgres and
initdb, then the error message showed up for running the db. How to fix
the problem?

LizheXusComputer:/Users/lizhexu pgsql$ /usr/local/pgsql/bin/postgres -D
/usr/local/pgsql/data >logfile 2>&1 &
[1] 17837
LizheXusComputer:/Users/lizhexu pgsql$ su: logfile: Permission denied

[1]+ Exit 1 /usr/local/pgsql/bin/postgres -D
/usr/local/pgsql/data >logfile 2>&1
LizheXusComputer:/Users/lizhexu pgsql$ su lizhexu
Password:
LizheXusComputer:~ lizhexu$ /usr/local/pgsql/bin/postgres -D
/usr/local/pgsql/data >logfile 2>&1 &
[1] 17842
LizheXusComputer:~ lizhexu$ /usr/local/pgsql/bin/createdb test
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 "/tmp/.s.PGSQL.5432"?
[1]+ Exit 2 /usr/local/pgsql/bin/postgres -D
/usr/local/pgsql/data >logfile 2>&1

Thank you very much.

L