Usefull web site: https://help.ubuntu.com/community/PostgreSql

1) assumed postgres installed.....try to see if pgadmin3 is too....
rich@rich-desktop:/$ pgadmin3
The program 'pgadmin3' is currently not installed.  You can install it by typing:
sudo apt-get install pgadmin3
bash: pgadmin3: command not found

2) installed pgadmin3

rich@rich-desktop:/$ sudo apt-get install pgadmin3
[sudo] password for rich:
Reading package lists... Done
Building dependency tree       
Reading state information... Done
The following packages were automatically installed and are no longer required:
  linux-backports-modules-2.6.24-21-generic libdns35 octave3.0-htmldoc
Use 'apt-get autoremove' to remove them.
The following extra packages will be installed:
  pgadmin3-data
Recommended packages:
  pgagent
The following NEW packages will be installed:
  pgadmin3 pgadmin3-data
0 upgraded, 2 newly installed, 0 to remove and 69 not upgraded.
Need to get 4206kB of archives.
After this operation, 12.2MB of additional disk space will be used.
Do you want to continue [Y/n]? Y
Get:1 http://de.archive.ubuntu.com hardy/universe pgadmin3-data 1.8.2-0ubuntu1 [1070kB]
Get:2 http://de.archive.ubuntu.com hardy/universe pgadmin3 1.8.2-0ubuntu1 [3136kB]
Fetched 4206kB in 6s (680kB/s)                                                 
Selecting previously deselected package pgadmin3-data.
(Reading database ...
dpkg: serious warning: files list file for package `gprolog' missing, assuming package has no files currently installed.
229768 files and directories currently installed.)
Unpacking pgadmin3-data (from .../pgadmin3-data_1.8.2-0ubuntu1_all.deb) ...
Selecting previously deselected package pgadmin3.
Unpacking pgadmin3 (from .../pgadmin3_1.8.2-0ubuntu1_i386.deb) ...
Setting up pgadmin3-data (1.8.2-0ubuntu1) ...
Setting up pgadmin3 (1.8.2-0ubuntu1) ...

 3) run pgadmin3 ... showed no databases....and threw multiple gtkPizza messages.....

rich@rich-desktop:/$ pgadmin3

(pgadmin3:7980): Gtk-WARNING **: /build/buildd/gtk+2.0-2.12.9/gtk/gtkwidget.c:8547: widget class `GtkPizza' has no property named `row-ending-details'

4) change password 

rich@rich-desktop:/$ sudo -u postgres psql postgres
Welcome to psql 8.3.9, the PostgreSQL interactive terminal.

Type:  \copyright for distribution terms
       \h for help with SQL commands
       ? for help with psql commands
       \g or terminate with semicolon to execute query
       \q to quit

postgres=# \password postgres
Enter new password:
Enter it again:
postgres=# quit
postgres-# exit
postgres-#
postgres=# sudo -u postgres createdb mydb
postgres-# \q
rich@rich-desktop:/$

5) created a database.....

rich@rich-desktop:/$ sudo -u postgres createdb mydb
rich@rich-desktop:/$

6) re-ran pgadmin3,

rich@rich-desktop:/$ pgadmin3

in gui, I "added server": File > Add Server and entered "localhost"

back in another terminal.....

7) create an expdba user and expd database:

rich@rich-desktop:/$ 

rich@rich-desktop:~/Desktop$ sudo -u postgres createuser -D -A -P expddba
Enter password for new role:
Enter it again:
Shall the new role be allowed to create more new roles? (y/n) y

 8) create an expd database:

rich@rich-desktop:~/Desktop$ sudo -u postgres createdb -O expddba expd

rich@rich-desktop:~/Desktop$