Writing parts

If writing soprano and alto on the same clef, is there a way to get one part to hold out a note while another sings at the same time? The program won't let me put notes of different values on top of each other. I would like a whole note hold while I have moving quarter notes below it. The only way to make the program do that is add a system for each part or write in each quarter note and tie them together. That makes the music look confusing and cluttered.