Aussie.zone is the server that you created your account on, think of it like having a yahoo email address. Some people have Gmail, some have outlook or iCloud, some have their own private domain. It really doesn’t matter too much because everyone can talk to everyone else, generally. Local is just every community hosted on Aussie.zone. All is everyone else and every other community in every other server that Aussie.zone is federated to (hasn’t blocked). Discover ability is certainly a problem and I’ve been here for two years and haven’t figured that out except stumbling on new communities on all just like you. You’ve pretty much got a handle on it it seems, I would just suggest a good client like Voyager to make things more intuitive on touchscreens if that’s what you’re looking for.