You are wrong.
It is true you use a browser to configure the setup but there is no internet involved only local network.
You access the administrative interface using the systems network address e.g. 192.168.1.10:9090 and that is all there is to it.
It works much the same way you can configure your printer using a browser application.
It can be fairly easy to setup - but reading guides on the internet will only complicate your efforts - mostly because the guides you read has not all been written by users who understand what they are doing - they are well intended - but complicates matters by adding settings which may be irrelevant for your setup.
I have written a step by step guide for simple office setup
The most basic example I can think of is