How websites are build using python..

Answer 1

https://www.djangoproject.com

Answer 2

Search for Web frameworks for python.
The most popular is Django. It has a great community and support. I also like it since it helps your to structure your project in the right way.
You can try Flask which is a very lightweight but still cool and popular web framework.
Also Tornado is worth to try, since it has some interesting concepts about io blocking calls.
And there are much more. But recommendation is start with Django.