How to set up a transition from one application to another?

Question

Django

Good evening, can you tell me how to make a transition from one sentence to another in Django.

From the main application 127.0.0.1:8000 , they go to all applications without problems, but when, for example, I want to go from products to another, it does not find the page because it does not see the /shop/contacts/ application. How can I make it go to the application /contacts/ Tell me the documentation or how to do it, thanks in advance.