Writing web apps involves wrangling a lot of warty technologies. If you try to grapple with them all simultaneously, it's going to feel like a quagmire. You should try to limit the number of unknowns and leverage the thing you know, Python, in order to start getting some positive reinforcement from success as soon as possible. So do the Django tutorial: https://docs.djangoproject.com/en/dev/intro/tutorial01/

Then explore some commonly used Django apps (the Django term for reusable modules) at https://www.djangopackages.com and make something simple. Add easy user accounts with https://github.com/bread-and-pepper/django-userena or https://github.com/pinax/django-user-accounts.

Other people may point out that Django isn't the best framework, and they will be correct, but I don't think that matters right now as much as working in a language you already know. If you said you already knew Ruby, my answer would be different.