sump up of setting up amp-jekyll in my project

I am working on a jekyll project and already asked some questions on stackoverflow and jekyll talks site. This post is a sump up for the issue I have about setting up amp-jekyll. amp-Jekyll is a jekyll plugin. The full documentation is at this adress :

The tree of my project is the following

enter image description here

My Version of jekyll is jekyll-3.6.2 I installed the plugin using the Gemfile (gem "amp-jekyll", "1.0.2" # installed). I checked that the plugin is well installed. Then I followed the documentation:

1) I Placed the layout file (amp.html at to the _layouts folder. I have a first question about that. I looked at this file and don't know how to use it. Have I just to copy it in the _layouts folder and that's all or have I to take a part of it and copy it to another file (and if so where ?). I can see in the body part the use of {{ header | amp_images }} or {{ footer | amp_images: false, 24, 24 }}. What does that mean ? . And what about the part included in head tag ?

2) Then, I Added amphtml-link to post heads (Add CSS styles to the html template). In my case I just copy the following code

{% if page.path contains '_posts' %}
  <link rel="amphtml" href="https://localhost::4000/inger/toto.html">
{% endif %}

with a faked href url in my footer.html file ( I have a second question about this snippet of code. What is this link ? and is it taken into consideration if this page a post ?

3) And I run bundle exec jekyll serve

The first page witch is published is index.html. the code is

layout: default
title: Hank Quinlan, Horrible Cop
lang: fr
<div class="blurb">
    <h1>This is content</h1>

The default.html file (in _layouts folder) is the following

<!DOCTYPE html>

{% include header.html %}

{{ content }}

{% include footer.html %}

And the header.html is at the following location : The first images that I display (and that I can't see) are in this file.

So my main question is : Why I can't see the images ?

Thank you in advance for your answer