A. You need to use following commands.
=> adduser – UNIX/Linux adduser command to add a user to /etc/passwd file

=> psql => It is a terminal-based front-end to PostgreSQL.

=> CREATE USER – Adds a new user to a PostgreSQL database cluster.

=> CREATE DATABASE – create a new database

=> GRANT ALL PRIVILEGES – define access privileges

Procedure to add a user to PostgreSQL database

To create a normal user and an associated database you need to type the following commands. The easiest way to use is to create a Linux / UNUX IDENT authentication i.e. add user tom to UNIX or Linux system first.

Step # 1: Add a Linux/UNIX user called tom

Type the following commands to create a UNIX/Linux user called tom:
# adduser tom
# passwd tom


Step # 2: Becoming a superuser

You need to login as database super user under postgresql server. Again the simplest way to connect as the postgres user is to change to the postgres unix user on the database server using su command as follows:
# su - postgres

Step #3: Now connect to database server

Type the following command
$ psql template1
OR
$ psql -d template1 -U postgres
Output:

Welcome to psql 7.4.16, the PostgreSQL interactive terminal.
Type:  copyright for distribution terms
       h for help with SQL commands
       ? for help on internal slash commands
       g or terminate with semicolon to execute query
       q to quit
template1=#

Step #4: Add a user called tom

Type the following command to create a user called tom with a password called myPassword (you need to type command highlighted with red color):
template1=# CREATE USER tom WITH PASSWORD 'myPassword';

Step #5: Add a database called jerry

Type the following command (you need to type command highlighted with red color):
template1=# CREATE DATABASE jerry;
Now grant all privileges on database
template1=# GRANT ALL PRIVILEGES ON DATABASE jerry to tom;
Type q to quit:
template1=# q

Step #6: Test tom user login

In order to login as tom you need to type following commands. Login as tom or use su command:
$ su - tom
$ psql -d jerry -U tom

Output:

Welcome to psql 7.4.16, the PostgreSQL interactive terminal.
Type:  copyright for distribution terms
       h for help with SQL commands
       ? for help on internal slash commands
       g or terminate with semicolon to execute query
       q to quit
jerry=>

source:http://www.cyberciti.biz/faq/howto-add-postgresql-user-account/