Since Arms is specifically for the Nintendo Switch and one can play on said Console System in a variety of ways, there are a number of different possible controls for playing the game. The main difference between the controls a player will have to use really depends on whether they are playing with two detached JoyCons, one detached JoyCon, attached JoyCons, or by using the Pro Controller.
2 Detached JoyCons Controls
Move: Tilt Both JoyCons
Punch / Use Arm: Punch Forward With Left OR Right JoyCon
Steer Left Arm: Tilt Left JoyCon
Steer Right Arm: Tilt Right JoyCon
Block: Tilt Both JoyCons Inwards
Grab: Punch Forward With Both JoyCons
Dash: Left JoyCon Bumper (L)
Jump: Right JoyCon Bumper (R)
Start Rush: Either Trigger (ZL/ZR)
1 Detached JoyCon / Attached JoyCons / Pro Controller Controls
Move: Left Analog JoyStick
Punch / Use Left Arm: Bottom Button (B/A/Down Arrow) OR Left Trigger (ZL)
Punch / Use Right Arm: Right Button (A/X/Right Arrow) OR Right Trigger (ZR)
Steer Arms: Left Analog JoyStick
Block: Push In On Left Analog JoyStick
Grab: Press BOTH Arms Button At Once
Dash: Left Button (B/X/Left Arrow)
Jump: Top Button (X/Y/Up Arrow)
Start Rush: Left Bumper (L/SL)
Select Target: Press Digital Stick Down