It's easy, just modify this line :

c_move(my,vector((key_w-key_s)* moveSpeed*time_step,0,0),nullvector,GLIDE);

While holding 'W' object walk forward, 'S' walk backward and
stop while none of them are pressed.

And add this line to turn if you like :

c_rotate(my,vector((key_a-key_d)* moveSpeed * time_step,0,0),USE_AXIS);

Pressing 'A' and 'D' to turn left and right.