what AH & RMAH?

sorry. not used to this short sentenses

last time when play D1 and D2 12 years ago, no such thing as this. That time battle.net is free for all and everyone play blizzard games come joining from around the world and play. then after battle.net shut down due to overwhelming players that purchased pirated D1 and D2, now all blizzard product must purchase legally and use battle.net for autohrization genuine copy. good example is WoW and newewst game, D3

does it mean that purchasing all those stuff (weapon, armour, accessories) use visa/mastercard? hmm... sound similar like purchasing android/ios games from google play/appstore

what's paragon level?

hmm.. if AH = Auction House, i guess RMAH =  REAL MONEY Auction House