After the stunning entrance sequences - which emulate and remix that of the original Ruby/Sapphire - you will arrive at the title screen. Press Start to begin gameplay.
You’ll go straight into the introductory sequence. Professor Birch will tell you about the Pokémon world in a manner akin to how he did on Ruby and Sapphire - you’ll only get the reference if you actually played those games, though.
During it, you’ll be told to tell Birch whether you are a boy or a girl: unlike Pokémon X/Y, you must deal with the characters’ set appearances. You’ll also be asked to give your name. Pick wisely for both, as you cannot alter your choice later on.
Once everything’s decided, it’s time to jump into your adventure, where new friends and experiences await you… Let’s go!