No route matches [GET] "/posts/new" - ruby-on-rails

Question

I am completely new to ruby, andI am following this ruby rails tutorial step by step, except for the detail that I've called my app "cinema".
I created a resource named "posts", there is a controller class called posts controller. From the page posts/new I should post a text with title, and execute an action (show). I am trying to add the show action in the routes file and in the controller class.
The show action should be called when a form is submitted, the form includes a title and a text field, mapped into the database.
In paragraph 5.7, there is a non-clear instruction: it says to add this line:
post GET /posts/:id(.:format) posts#show
To my routes.rb file, but it doesn't say where to write it exactly, I put it under resources:posts (maybe it's the wrong place, it doesn't saying anything about that).
I also added the show method to the controller class:
def show
#post = Post.find(params[:id])
end
private
def post_params
params.require(:post).permit(:title,:test);
end
But when I submit the form I still get this error:
The rake routes command result:
Prefix Verb URI Pattern Controller#Action
welcome_index GET /welcome/index(.:format) welcome#index
root GET / welcome#index
posts GET /posts(.:format) posts#index
POST /posts(.:format) posts#create
new_post GET /posts/new(.:format) posts#new
edit_post GET /posts/:id/edit(.:format) posts#edit
post GET /posts/:id(.:format) posts#show
PATCH /posts/:id(.:format) posts#update
PUT /posts/:id(.:format) posts#update
DELETE /posts/:id(.:format) posts#destroy

Answer 1

It doesn't tell you to add it to routes.rb. It's one of the routes that is created automatically with:
resources :posts
Remove the line from your routes.rb restart the server and continue with the tutorial.
Tip: you can run rake routes to see all available routes in your application.

Answer 2

Your whole question seems completely contradictory to me.
You never do this in rails routes -
post GET /posts/:id(.:format) posts#show
Instead in routes.rb file.
get 'posts/:id' => 'posts#show'
The routing is done on a priority basis (first come first serve), so if your are adding get 'posts/:id' after the resources :posts, it is of no use as resources :posts already does it for you (read the rails routing guide on resources).
Your form submission should be a post data, if you are using resources 'new' should be a 'get' data and the corresponding 'post' should be 'create'. Your 'new' route has an error, then where else are you rendering your form to submit the form data?
My suggestion is that you keep the 'resources :post' and remove every other this corresponding to your :post from routes file. If you have everything else right then it should probably work fine.

Answer 3

resources :posts
delete it
rails s
paste resources :posts
rails s
I make it and success