This is the basic setup for our zone defense. We are defense and red; the blue team is playing down, towards the end zone at the bottom of the screen. Our player 1 is the mark. In this initial setup the disc is in the middle of the field (with offensive player 1) so the marker forces a forehand throw. Defensive player two is the apex. Together these two form the "cup". The apex has to stand outside a 10 foot circle centered on the person who has the disc; she positions herself so that there is no throw in between the mark and the apex. (When viewed from the disc, the left hand of the mark and the right hand of the apex overlap.) Together, the cup restricts the throws that are possible pretty severely: offensive player 1 can throw back, to player 2, or to the right, to player 3. The next two players are defending players 3 and 4: they are the left and right wing, respectively. It is these players' jobs to block offensive players that enter their zone: the left wing's zone is the left 40% of the field, starting roughly where the apex is and extending maybe 30 ft back from there. The right wing's zone is the right 60% of the field, also roughly 30 ft from the apex down. You'll notice that player 4 is standing in an area where the disc is not likely to go, because of the mark and the apex blocking those throws; that's why his zone is larger. Finally, player 5 is the deep defender. Her zone is everything behind the wings.
Whenever the disc travels, we have to re-establish our field positions as quickly as possible. In this case, the disc went to a position closer to the apex than the mark; in that situation the apex and the mark switch roles. This will probably happen more often than not; the mark and apex switch roles very frequently. The (new) mark applies very strict force along the line - meaning, it should be relatively easy to throw up or down the line but almost impossible to throw into the field. The apex blocks the throw down the line; the left wing blocks longer throws down the line; deep blocks very long throws down the line. The right wing stays somewhere in the disc-shadow of the mark and apex.
If the thrower manages to throw into the field, one of the wings may need to mark for a few seconds while the cup is running towards the disc.
As soon as the cup has arrived, the right wing takes his regular position. Because we're now on the right side of the field, positions are mirrored relative to step 2: the mark forces a backhand throw, and the right wing has a narrower zone than the left wing.
It's very important to communicate with your team mates. If the deep player sees someone leaving her zone to make a cut, she should let the appropriate wing know. In this case, she'd shout: "Cut right!"
Another standard offensive play is to run into the cup, a.k.a. crashing the cup, for a very short pass. One of the wings should notice this being about to happen and warn the apex: "Crash left!"
We'll let our opponents reset to a standard position in the middle of the field.
Within the zone you are defending, you need to deal with any offensive players that are entering it: here, the left wing blocks a play to offensive player 3.
If the left wing is drawn to the left and another player comes from the right, for example, the right wing can come a bit closer to the left zone.
If both offensive deep players come forward, the deep defender can come forward. But if one of them stays deep, the deep defender should stay deep too. Nonetheless, the two wings should be able to block almost all possible passes to the three players coming up the left wing here.