Docker container URL mapping

I'm new to traefik v2, and I need to make it work as a standalone reverse proxy for now (used to traefik v1 under Kubernetes). Traefik is running OK on my host, and I can see the dashboard and api rawdata without any problem.

Now I want to set up a second container (let's say rancher). So I deployed rancher as a second standalone container, and it appeared in Traefik dashboard, showing that my traefik installation is working. But how can I now say to traefik how to reach this second container via a path, like:

Traefik URL:

Required Rancher URL: to point to the right container, while removing the /rancher part, obviously.

I just don't understand yet how to make it work