So, this is the way you make sessions/logins work in ruby:

class SessionController < ApplicationController
  def login
    @session['logged'] = true
  end
  def logout
    @session['logged'] = false
  end
end

The @session variable is available anywhere. Use it anywhere. For example you could come up with the following view showing whether the user is logged in:

<p>Logged in: <%= @session['logged'] %> </p>

And that is it. Anything beyond that (like adding a User model etc.) is out of this post's target. There are many articles on those things yet no clear explanation where to find and how to init a session. As you can see - the answer is clear - you don't The session is already there. Just start using it.