@mapu @Sunshine I think the best way to learn JOSM is just to start using it, and work out how to do things as you need to. I still kick myself every now and again when I discover some new feature I didn't know about. Do check out the different modes at https://josm.openstreetmap.de/wiki/Help/Menu/Mode though. In particular, 'W' mode is awesome for correcting/improving the geometry of ways.