There is only one class in Django which is User, different types of users are instances of this class with other special attributes set.
Main attributes are: username, password, email, first_name, and last_name. However, there are others.

Using create_user function:

from django.contrib.auth.models import User
user = User.objects.create_user('john', 'lennon@thebeatles.com', 'johnpassword')
# At this point, user is a User object that has already been saved to the database. 
user.last_name = 'Lennon'
user.save()

To change user passwords we'll do:

from django.contrib.auth.models import User
u = User.objects.get(username='john')
u.set_password('new password')
u.save()

User authenticate(), it takes credentials from keyword arguments and returns a User object if they were valid, if not returns None.