data travelling between controller and embedded ruby file(ruby on rails)

Question

I'm just beginning to learn Ruby on Rails. One thing I'm having real trouble understanding is how data is transferred from the .html.erb file to the controller file.

Consider the following new.html.erb

<%= form_for :post, url: posts_path do |f| %>
  <p>
    <%=f.label :title %>
    <%=f.text_area :title %>
  </p>
  <p>
    <%=f.label :body %>
    <%=f.text_area :body %>
  </p>
  <p>
    <%=f.submit %>
  </p>
<% end %>

and then there's my controller file, posts_controller.rb

class PostsController < ApplicationController

  def index
    @post=Post.all
  end

  def new
  end

  def create
    @post=Post.new(post_param) #
    @post.save
    redirect_to @post
  end

  def show
    @post=Post.find(params[:id])
  end

  private 

  def post_param
    params.require(:post).permit(:title, :body)
  end

end    

Okay now so the part that I don't understand.

1. How does the create method get the value for 'post'.
2. Can you explain what <%= form_for :post, url: posts_path do |f| %> actually does?

Answer 1

form_for sends an http POST request directed at the posts_path. Your routes file probably says something like "resources :post", which automatically directs any http POST requests to the "create" method in your controller. Inside this POST request, all the data you entered into the form will be inside the params variable.