I have a Kenmore stackable washer and dryer. It shreiked and shrilled for a long time. We decided to take it apart and ordered parts that we thought we might need and actually put it back together except we cannot figure out how to put the belt on the drum and have it be snug. There is some slack and we can't figure out how to tighten it up.

You should find a pulley between the drum and the pulley on the motor. That second pulley should press againist the belt and be held tight by a spring. The spring may have fallen off during your belt removal.

You should find a pulley between the drum and the pulley on the motor. That second pulley should press againist the belt and be held tight by a spring. The spring may have fallen off during your belt removal.
That answer is correct, except that the spring is now part of the pulley system and the "fixer" is probably not putting the belt around the tension pulley the correct way!