Django: How to create a new CustomUser with custom registration form

I am trying to make a custom registration form in Django, using HTML and CSS and not Django's form.as_p. I have the following code in views.py:

def register(request):
   if request.POST:
       username = request.POST['username']
       email = request.POST['email']
       password = request.POST['password']
       password_confirm = request.POST['password-confirm']
       if(valid_form(username, email, password, password_confirm)) {
          #create the new user
       } else {
          #send some error message
       }    
return render(request, 'index.html')

I have my own function valid_form to check if the form fields entered by the user are valid. However, I am not sure how I can create the new user using a custom User Model. In all of the code examples regarding registration forms I have seen something like this:

def register(request):
if request.method == 'POST':
    form = UserCreationForm(request.POST)
    if form.is_valid():
        form.save()
        return redirect('main-page')
else:
    form = UserCreationForm()
return render(request, 'users/register.html', {'form': form})

Where form.save() is used to create the new user. I have the following model for a user in models.py:

from django.contrib.auth.models import AbstractUser
from django.db import models

class CustomUser(AbstractUser):
    id = models.AutoField(primary_key=True)
    username = models.CharField(max_length=200, null=True)
    email = models.EmailField(max_length=70, null=True)

How can I create a new CustomUser after validating form data? Any insights are appreciated.