If you installed postresql on your server then just host: localhost to database.yml, I usually throw it in around where it says pool: 5. Otherwise if it's not localhost definitely tell that app where to find its database.
development:
adapter: postgresql
encoding: unicode
database: kickrstack_development
host: localhost
pool: 5
username: kickrstack
password: secret
Make sure your user credentials are set correctly by creating a database and assigning ownership to your app's user to establish the connection. To create a new user in postgresql 9 run:
sudo -u postgres psql
set the postgresql user password if you haven't, it's just backslash password.
postgres=# \password
Create a new user and password and the user's new database:
postgres=# create user "guy_on_stackoverflow" with password 'keepitonthedl';
postgres=# create database "dcaclab_development" owner "guy_on_stackoverflow";
Now update your database.yml file after you've confirmed creating the database, user, password and set these privileges. Don't forget host: localhost.