Add a coment in a post ( how can I do)?

I'm coding my personal website , I have a backoffice where I can write blog_post ( title , content , category and date ).
I would like to make user comment my blog post without being logged in .
This is the code in /layouts/home.html.erb.

<section class="blog id col-sm-12">




<h1 class="col-sm-10 col-sm-offset-2 text-left">Blog post</h1>



      <div class="col-sm-2"></div>

                    <% @blog_posts.each do |blog_post| %>

                      <div class="col-sm-5  blog_post ">

                                <div class="col-sm-12 post">

                        <h3 class="col-sm-12 text-left"><%= blog_post.title.capitalize  %></h3>

                            <span class="col-sm-1" style="background-color:white;"></span>

                              <p class="col-sm-12 text-left content">"<%= blog_post.description.capitalize %>"</p>

                              <p class="col-sm-8 text-left"> <i class="fa fa-circle" style="color:#F0F4C3;"> <%= blog_post.category.capitalize %></i></p>

                              <p class="col-sm-4 text-right"> <%= blog_post.post_date  %> </p>

                              <p class="col-sm-12 text-left content">"<%= blog_post.comments.count %>"</p>

                              </div>


                <p class="col-sm-6  btn-default text-center post_button"><%= link_to 'Visualizza', blog_post %></p>

                <p class="col-sm-6 btn-default text-center post_button comment"><a href="#0">Commenta</a></p>


            </div>

<div class="col-sm-2"></div>

      <% end %>

<% if admin? %>

<% end %>

This is the section that comes out if an user click on "blog" , at the ond of if there is a button with "commenta", clicking it appears  a modal with 3 fields , name , email and comment. 

Comments belong to blog post and blog post has many comments obviously, I know I should set something in the controller but i really don't know what .
I had some suggestions but everybody told me how to make user add a comment in blog_post #show , but i would like to make them comment directly from the homepage.

Every advice is good :D