Hitbox replaces the directional arrows with four buttons. So the three smaller gold buttons would be your left, down, right, and the larger gold button is your up/jump button. That larger button can be pressed by either thumb.
This layout can be imitated on a keyboard with ASD + spacebar. For a 2D game like Street Fighter, the hitbox layout is more ergonomic because if you use WASD, you have one finger for both up and down.
Some people use actually WASD with their setup. That's called a mixbox.
