It makes sense when a user creates an account, especially when an email confirmation is required, that the user is redirected to a welcome page letting them know they need to check their email to confirm registration. Or, if a user logs in, you probably want to redirect them to a page other than the root URL.
Devise is a powerful authentication system for Rails applications. This tutorial walks you through setting up devise, as well as setting up your user MVC. Follow along with the code sample on GitHub.