You can place the notes or rests at one of 4 voices. To determine the voice select the voice number on voice selector ().

Because multiple voices can be very confusing there is a color button (), which causes the notes and rests to be drawn colored:

The colors refer to the colors of the voice selector.

The normal case is: Every voice produces the same sound (plays the same instrument) during replay. But you can change this behaviour by attaching different sounds to different voices.