What is the best way to register in djnago?

Question

Django

The first time you run the migrate command, django creates several tables in the database, including auth_user. This is where user data is stored. But what if I need more data to be there? For example, if I need a phone number: is it better to create a new field in this table or create a new table with phone numbers associated with auth_user? Or maybe it's better to create your own table with users and register them using procedures in the database, and not something like this:

def signup(request):
    if request.method == 'POST':
        form = SignUpForm(request.POST)
        if form.is_valid():
            form.save()
            username = form.cleaned_data.get('username')
            my_password = form.cleaned_data.get('password1')
            user = authenticate(username=username, password=my_password)
            login(request, user)
            return redirect('home')
    else:
        form = SignUpForm()
    return render(request, 'signup.html', {'form': form})

One more question:

{% if user.is_authenticated %}
<form id="logoutForm" action="/logout" method="post" class="navbar-right">
    {% csrf_token %}
    <ul class="nav navbar-nav navbar-right">
        <li><span class="navbar-brand">Hello {{ user.username }}!</span></li>
        <li><a href="javascript:document.getElementById('logoutForm').submit()">Log off</a></li>
    </ul>
</form>

{% else %}

<ul class="nav navbar-nav navbar-right">
    <li><a href="{% url 'login' %}">Log in</a></li>
</ul>

{% endif %}

{% if user.is_authenticated %}#откуда django вообще берет user, если я этого не в одной функции не передаю?

works with standard auth_user table? Then, if you make everything custom, will it need to be passed through context as a variable? How then to make sure that after reloading the page or after redirecting the user does not crash? And do they often do authentication in a non-standard way (LoginView)?

PS

посмотрел много уроков и на русском и на английском - ничего чтобы мне помогло бы не нашел