How does it work?
It is fairly simple as how the stuff works: Download the newest version of multiworld from Github and create a bunch of seeds for you and your friends. LetsMultiworld! does the part of the server.
There is a video made by Luhna_LP on Youtube, which shows the setup and configuration for multiworld (including multiserver, which's part is done by LetsMultiworld!). It can be found here (german video!).