django code doesnt work after adding a new app code example

Example 1: start django

pip install django # Install Django Packages
django-admin startproject project_name # Create a Project
cd project_name
python manage.py makemigrations # Create new migrations
python manage.py migrate # Apply Migrations
python manage.py createsuperuser # Create User for admin
python manage.py runserver # Start Server

python manage.py startapp sub_module # Create a sub app

Example 2: django-admin startproject

$ django-admin <command> [options]
$ manage.py <command> [options]
$ python -m django <command> [options]