The 3DS has a touch screen instead of an arcade-spec joystick, which makes it a bit less than optimal for fighting games like Super Street Fighter IV 3D Edition. But in bringing the fighter to 3DS, Capcom has done its best to concoct a little touch-screen-ade.
The game's website details the touch screen implementation, which allows players to assign their choice of moves to four sections of the screen. You can set things like Focus Attacks, special moves, Ultra Combos, or combinations of three simultaneous button presses, according to the examples shown.
Capcom has been known to make concessions like this for systems without ideal fighting game controllers. SNK vs. Capcom EO on GameCube allowed players to launch special moves by pressing directions on the right stick, for example, and Tatsunoko vs. Capcom had optional simplified controls for use with the Wiimote and Nunchuk.