noise() always returns a value between 0-1 depending on the coordinate that is given as a parameter.
noise(0) returns a value and if you call
noise(0) again, you get the same value again. If you call
noise(0.01) you get a new value. The graph below shows a
noise(x) curve, i.e. the value of noise on y-axis at the corresponding x-value.
Depending on how much you increment x each frame the values will be smoother or more random.