Installed Postgres using apt-get

Just login as unix user "postgres" by :
setting unix user password
$ sudo passwd postgres

login as it
$ su postgres

create postgres user by
$ createuser pgusername

with options can be seen here http://www.postgresql.org/docs/current/static/app-createuser.html
create postgres database by
$ createdb pgusername

then use the postgres cli or pgcli(python package with autocomplete) to test