World War Z pits you and up to three other players against some pretty impressive zombie hordes. You will be armed with a range of primary, secondary, and heavy weapons, but you will also have some Defense Systems at your disposal.
How To Use Defense Systems
Defense Systems can be found lying around the various levels, normally at parts that are about to become an absolute mosh-pit of zombies. You can find them in large crates that will be marked as Tools. Just interact with the crate to pick up the item inside, but remember that you can only carry one at a time.
Now, have a look around the area, and you should be able to see a few options marked on the ground for where you can place that particular Defense System.
Think carefully about where you place it, as you will want it to impact as many zombies as possible. All you have to do is run up to the ghostly outline of the Defense System and interact with it to place the actual Defense System there. It can also make a lot of sense to have Defense Systems laid out close together. For example, the Bared Wire will slow down enemies, and a nearby Automated Turret can then pick them all off before they reach you.
Clever use of Defense Systems can make challenging parts of the game much easier, so make sure you are paying attention to your surroundings, and taking advantages of all the options that Defense Systems can offer to you and your team.