Heroku is a PAAS (Platform As A Service) for Ruby on Rails. You will get a free domain with limited support for your Rails App. After signup to Heroku, you can install the gem:

gem install heroku

Then you can start your application with create command:

heroku create yourapp

Using git commands you can deploy this app to the Heroku:

git add, git commit,

git push heroku master

This will deploy to your heroku repository, git @heroku.com:yourapp.git
And your URL will be, http://yourapp.heroku.com

To do the db:migrate run the command:

heroku rake db:migrate

For more details visit Heroku