What I did:
sudo -u postgres psql
CREATE ROLE shop CREATEDB LOGIN PASSWORD 'kurt1245';
Then I cloned a repository from GitHub (a rails application which uses pg), bundle install, edit database.yml to write my password and now after rake db:create (also setup and migrate) doesn't work.
database.yml:
development:
adapter: postgresql
encoding: unicode
database: shop_development
pool: 5
username: shop
password: kurt1245
test:
adapter: postgresql
encoding: unicode
database: shop_test
pool: 5
username: shop
password: kurt1245