That gif is very satisfying. It's far beyond my level of mapping.
OpenStreetMap community
Everything #OpenStreetMap related is welcome: software releases, showing of your work, questions about how to tag something, as long as it has to do with OpenStreetMap or OpenStreetMap-related software.
OpenStreetMap is a map of the world, created by people like you and free to use under an open license.
Join OpenStreetMap and start mapping: https://www.openstreetmap.org.
There are many communication channels about OSM, many organized around a certain country or region. Discover them on https://openstreetmap.community
https://mapcomplete.org is an easy-to-use website to view, edit and add points (such as shops, restaurants and others)
https://learnosm.org/en/ has a lot of information for beginners too.
I think that is why they shared the tutorial, since it is beyond what most people would attempt.
Once you have it set up it's a blast to use! It's just a few plugins for JOSM and once you have the hotkeys memorised you can map out rectangular buildings in seconds!