Handler setup in a zone, I will show the first part without defenders. This is because there are lot's of different zones but the basic handler set up is usually the same. Three handlers spread across the field. The two handlers on either side should always look to be forward slightly when the middle thrower has the disc, this is not a requirement and their are many situations when it's impractical, but if the defense is allowing it, then they should definitely look to be. Especially the open side handler.
When the disc moves to the sideline, the middle handler drops back, behind the thrower. This is so that there is two very different directions with which the Puppy/Chase/Cup have to try and stop, generally making them to choose one and leave the other open.
Swinging from side to side looks like this.
Now we add a puppy fense or 1-3-2-1 zone (just up the front). As you can see the puppy has to choose whether to stop the swing throw leaving the dump open...
Or the dump, leaving the swing open.
If the middle handler doesn't drop behind the thrower, you can see how the puppy can make both the dump and the swing throw difficult
for a 2-3-2 the procedure is the same.
This time the y chose to leave the swing open (not a good choice btw). but you can see how if the middle handler hadn't dropped behind, that throw would be much harder to make.