注意事項はこちら。
https://qiita.com/K-Kazutaka/items/1a432bda4f723e6757d6
写経用の記事です。

blogディレクトリの下にforms.pyというファイルを作成する。

blog/forms.py

from django import forms

from .models import Post

class PostForm(forms.ModelForm):

    class Meta:
        model = Post
        fields = ('title', 'text',)

blog/templates/blog/base.html

{% load static %}
<html>
    <head>
        <title>Django Girls blog</title>
        <link rel="stylesheet" href="//maxcdn.bootstrapcdn.com/bootstrap/3.2.0/css/bootstrap.min.css">
        <link rel="stylesheet" href="//maxcdn.bootstrapcdn.com/bootstrap/3.2.0/css/bootstrap-theme.min.css">
        <link href='//fonts.googleapis.com/css?family=Lobster&subset=latin,latin-ext' rel='stylesheet' type='text/css'>
        <link rel="stylesheet" href="{% static 'css/blog.css' %}">
    </head>
    <body>
        <div class="page-header">
            <a href="{% url 'post_new' %}" class="top-menu"><span class="glyphicon glyphicon-plus"></span></a>
            <h1><a href="/">Django Girls Blog</a></h1>
        </div>
        <div class="content container">
            <div class="row">
                <div class="col-md-8">
                    {% block content %}
                    {% endblock %}
                </div>
            </div>
        </div>
    </body>
</html>

blog/urls.py

from django.urls import path 
from . import views

urlpatterns = [
    path('', views.post_list, name='post_list'),
    path('post/<int:pk>/', views.post_detail, name='post_detail'),
    path('post/new/', views.post_new, name='post_new'),
]

blog/views.py

from django.shortcuts import render
from django.utils import timezone
from .models import Post
from django.shortcuts import render, get_object_or_404
from .forms import PostForm

def post_list(request):
    posts = Post.objects.filter(published_date__lte=timezone.now()).order_by('published_date')
    return render(request, 'blog/post_list.html', {'posts': posts})

def post_detail(request, pk):
    post = get_object_or_404(Post, pk=pk)
    return render(request, 'blog/post_detail.html', {'post': post})

def post_new(request):
    form = PostForm()
    return render(request, 'blog/post_edit.html', {'form': form})

blog/templates/blogの中にpost_edit.htmlというファイルを作成。

blog/templates/blog/post_edit.html

{% extends 'blog/base.html' %}

{% block content %}
    <h1>New post</h1>
    <form method="POST" class="post-form">{% csrf_token %}
        {{ form.as_p }}
        <button type="submit" class="save btn btn-default">Save</button>
    </form>
{% endblock %}

blog/views.py

from django.shortcuts import render
from django.utils import timezone
from .models import Post
from django.shortcuts import render, get_object_or_404
from .forms import PostForm
from django.shortcuts import redirect

def post_list(request):
    posts = Post.objects.filter(published_date__lte=timezone.now()).order_by('published_date')
    return render(request, 'blog/post_list.html', {'posts': posts})

def post_detail(request, pk):
    post = get_object_or_404(Post, pk=pk)
    return render(request, 'blog/post_detail.html', {'post': post})

def post_new(request):
    if request.method == "POST":
        form = PostForm(request.POST)
        if form.is_valid():
            post = form.save(commit=False)
            post.author = request.user
            post.published_date = timezone.now()
            post.save()
            return redirect('post_detail', pk=post.pk)
    else:
        form = PostForm()
    return render(request, 'blog/post_edit.html', {'form': form})

blog/templates/blog/post_detail.html

{% extends 'blog/base.html' %}

{% block content %}
    <div class="post">
        {% if post.published_date %}
            <div class="date">
                {{ post.published_date }}
            </div>
        {% endif %}
        <a class="btn btn-default" href="{% url 'post_edit' pk=post.pk %}"><span class="glyphicon glyphicon-pencil"></span></a>
        <h1>{{ post.title }}</h1>
        <p>{{ post.text|linebreaksbr }}</p>
    </div>
{% endblock %}

blog/urls.py

from django.urls import path
from . import views

urlpatterns = [
    path('', views.post_list, name='post_list'),
    path('post/<int:pk>/', views.post_detail, name='post_detail'),
    path('post/new/', views.post_new, name='post_new'),
    path('post/<int:pk>/edit/', views.post_edit, name='post_edit'),
]

blog/views.py

from django.shortcuts import render
from django.utils import timezone
from .models import Post
from django.shortcuts import render, get_object_or_404
from .forms import PostForm
from django.shortcuts import redirect

def post_list(request):
    posts = Post.objects.filter(published_date__lte=timezone.now()).order_by('published_date')
    return render(request, 'blog/post_list.html', {'posts': posts})

def post_detail(request, pk):
    post = get_object_or_404(Post, pk=pk)
    return render(request, 'blog/post_detail.html', {'post': post})

def post_new(request):
    if request.method == "POST":
        form = PostForm(request.POST)
        if form.is_valid():
            post = form.save(commit=False)
            post.author = request.user
            post.published_date = timezone.now()
            post.save()
            return redirect('post_detail', pk=post.pk)
    else:
        form = PostForm()
    return render(request, 'blog/post_edit.html', {'form': form})

def post_edit(request, pk):
    post = get_object_or_404(Post, pk=pk)
    if request.method == "POST":
        form = PostForm(request.POST, instance=post)
        if form.is_valid():
            post = form.save(commit=False)
            post.author = request.user
            post.published_date = timezone.now()
            post.save()
            return redirect('post_detail', pk=post.pk)
    else:
        form = PostForm(instance=post)
    return render(request, 'blog/post_edit.html', {'form': form})

blog/templates/blog/base.html

{% load static %}
<html>
    <head>
        <title>Django Girls blog</title>
        <link rel="stylesheet" href="//maxcdn.bootstrapcdn.com/bootstrap/3.2.0/css/bootstrap.min.css">
        <link rel="stylesheet" href="//maxcdn.bootstrapcdn.com/bootstrap/3.2.0/css/bootstrap-theme.min.css">
        <link href='//fonts.googleapis.com/css?family=Lobster&subset=latin,latin-ext' rel='stylesheet' type='text/css'>
        <link rel="stylesheet" href="{% static 'css/blog.css' %}">
    </head>
    <body>
    <div class="page-header">
    {% if user.is_authenticated %}
        <a href="{% url 'post_new' %}" class="top-menu"><span class="glyphicon glyphicon-plus"></span></a>
    {% endif %}
        <h1><a href="/">Django Girls Blog</a></h1>
    </div>
    <div class="content container">
        <div class="row">
            <div class="col-md-8">
            {% block content %}
            {% endblock %}
            </div>
        </div>
    </div>
    </body>
</html>

blog/templates/blog/post_detail.html

{% extends 'blog/base.html' %}

{% block content %}
    <div class="post">
        {% if post.published_date %}
            <div class="date">
                {{ post.published_date }}
            </div>
        {% endif %}
    {% if user.is_authenticated %}
        <a class="btn btn-default" href="{% url 'post_edit' pk=post.pk %}"><span class="glyphicon glyphicon-pencil"></span></a>
    {% endif %}
        <h1>{{ post.title }}</h1>
        <p>{{ post.text|linebreaksbr }}</p>
    </div>
{% endblock %}