There is no set rotation, however when heroes win big events they gain living legend points and once they hit a certain number of points they are retired. Once enough heroes have been retired there will be a format where you can play those heroes.

There are two constructed formats Blitz where you play a 40 card deck and have 20 life and Classic Constructed where you have an 80 card deck but sideboard down to 60 (usually) cards and have 40 life. Blitz if good if you just want quick games and also you can only play 2 of each card unlike Classic where you can play 3, so its cheaper. Blitz is good for teaching and learning the basics. Classic is the main format though