The fundamental MVC pattern is unchanged! It would all be very familiar! Just fire up a new project and off you go! As for authentication, if you want a read

The fundamental MVC pattern is unchanged! It would all be very familiar! Just fire up a new project and off you go! As for authentication, if you want a ready to go solution, then Devise is still current and pretty much the default! Development of Gems like Attachinary are now deprecated in favour of Rails' Active Storage. I'm not an expert, but I still dip in and out, and find I can still get by with the basics I learnt back on v3! YMMV :-)