1. This installs the database server/client,some extra utility scripts and the pgAdmin GUI application for working with the database.

$ sudo apt-get install postgresql postgresql-client postgresql-contrib
$ sudo apt-get install pgadmin3

2. Now we need to reset the password for the ‘postgres’ admin account for the server,substitute in the password you want to use for your administrator account.

$ sudo su postgres -c psql template1
template1=# ALTER USER postgres WITH PASSWORD 'password';
template1=# \q

3. That alters the password for within the database,now we need to do the same for the unix user ‘postgres’.

$ sudo passwd -d postgres
$ sudo su postgres -c passwd

4. Set-up the Postgresql admin pack that enables better logging and monitoring within pgAdmin.

$ sudo su postgres -c psql < /usr/share/postgresql/9.1/extension/adminpack--1.0.sql

5. Edit the postgresql.conf file.

$ sudo gedit /etc/postgresql/9.1/main/postgresql.conf

Change the line:
#listen_addresses = 'localhost'
to
listen_addresses = '*'
and also change the line:
#password_encryption = on
to
password_encryption = on

6. Define who can access the server. This is all done using the pg_hba.conf.

$ sudo gedit /etc/postgresql/8.3/main/pg_hba.conf

add this text to the bottom of the file:
host all all [ip address] [subnet mask] md5
add in your subnet mask (i.e. 255.255.255.0) and the IP address of your server (i.e. 138.250.192.115).
Note:if you have some password error,please change all "md5" to "trust" in this file.

7. Now all you have to do is restart the server.

$ sudo /etc/init.d/postgresql restart

Reference:
http://hocuspokus.net/2008/05/install-postgresql-on-ubuntu-804/