The emulator can show both screens of the console in real time, or you can choose to see only one in full screen and assign a button to alternate between both. As for the controls, you can customize the touch buttons as you please, although your screen will most likely be filled with virtual controls. That said, Citra's official version supports external physical controllers.
Citra supports a large number of games from the Nintendo 3DS catalog, many of which have significantly better graphics than what you'd find on the original platform. Games like Pokémon Sun and Moon and The Legend of Zelda: A Link Between Worlds look incredible. You can even add graphic modifications to add higher resolution textures.
Citra is quite possibly the best and most advanced Nintendo 3DS emulator available for Android. We're talking about an open-source project created altruistically that lets you enjoy your laptop games from the comfort of your Android smartphone.