As far as the controls go, you can use either the keyboard or an external gamepad.
The emulator can display both screens in real time, though it's also possible to show only one in fullscreen and assign a button to alternate between the two. Citra is a Nintendo 3DS emulator for Mac that can run commercial games at 100% of their speed, in addition to adding a series of characteristics to improve their visuals above and beyond the modest resolution of Nintendo handheld consoles.
