The cursor works too, but you can't reach Space easily that way. Probably it advises to use A and D for control so that you can use your left hand for keyboard

The cursor works too, but you can't reach Space easily that way. Probably it advises to use A and D for control so that you can use your left hand for keyboard and right hand for mouse. On a second thought Up should work as space, and cursor keys would be fully usable.