Gatekeeper- Need more explanation on the configuration options

Trying to configure Gatekeeper to provide authentication for RTIR via Keycloak.
Unable to understand the configuration options given in the document.
I tried doing the setup as per the document but the gatekeeper is not able to redirect to keycloak’s login page for authentication.
Need more clarity on where to put Gatekeeper URL & the RTIR URL. I do have some confusion with few config options such as redirection-url, upstream-url, listen.

I am trying this setup on the local machine. I need to test in the development environment first.

Here are the versions that I am using-
Ubuntu 18.04
Keycloak version 8.0.1
The latest version of gatekeeper
RTIR: 4.4.4

Can someone please help?